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The inferior margin of the posterior axillary wall is the posterior axillary skin fold, which overlies the margins of the teres major muscle laterally and latissimus dorsi muscle medially.
The medial wall of the axilla is the upper part of the serratus anterior muscle overlying the thoracic wall. The long thoracic nerve passes vertically out of the axilla and down the lateral surface of the serratus anterior muscle in a position just anterior to the posterior axillary skin fold.
The lateral boundary of the axilla is the humerus.
The floor of the axilla is the dome of skin between the posterior and anterior axillary skin folds.
Major vessels, nerves, and lymphatics travel between the upper limb and the trunk by passing through the axilla.
The axillary artery, axillary vein, and components of the brachial plexus pass through the axilla and into the arm by traveling lateral to the dome of skin that forms the floor. This neurovascular bundle can be palpated by placing a hand into this dome of skin and pressing laterally against the humerus.
The cephalic vein travels in superficial fascia in the cleft between the deltoid muscle and the pectoralis major muscle and penetrates deep fascia in the clavipectoral triangle to join with the axillary vein.
Locating the brachial artery in the arm
The brachial artery is on the medial side of the arm in the cleft between the biceps brachii and triceps brachii muscles (Fig. 7.119). The median nerve courses with the brachial artery, whereas the ulnar nerve deviates posteriorly from the vessel in distal regions.
The triceps brachii tendon and position of the radial nerve
The triceps brachii muscle forms the soft tissue mass posterior to the humerus, and the tendon inserts onto the olecranon of the ulna, which is readily palpable and forms the bony protuberance at the “tip” of the elbow (Fig. 7.120).
The brachioradialis muscle is also visible as a muscular bulge on the lateral aspect of the arm. It is particularly prominent when the forearm is half pronated, flexed at the elbow against resistance, and viewed anteriorly.
The radial nerve in the distal arm emerges from behind the humerus to lie deep to the brachioradialis muscle.
The cubital fossa lies anterior to the elbow joint and contains the biceps brachii tendon, the brachial artery, and the median nerve (Fig. 7.121).
The base of the cubital fossa is an imaginary line between the readily palpable medial and lateral epicondyles of the humerus. The lateral and medial borders are formed by the brachioradialis and pronator teres muscles, respectively. The margin of the brachioradialis can be found by asking a subject to flex the semipronated forearm against resistance. The margin of the pronator teres can be estimated by an oblique line extending between the medial epicondyle and the midpoint along the length of the lateral surface of the forearm. The approximate apex of the cubital fossa is where this line meets the margin of the brachioradialis muscle.
Contents of the cubital fossa, from lateral to medial, are the tendon of the biceps brachii, the brachial artery, and the median nerve. The tendon of the biceps brachii is easily palpable. Often the cephalic, basilic, and median cubital veins are visible in the subcutaneous fascia overlying the cubital fossa.
The ulnar nerve passes behind the medial epicondyle of the humerus and can be “rolled” here against the bone.
The radial nerve travels into the forearm deep to the margin of the brachioradialis muscle anterior to the elbow joint.
Identifying tendons and locating major vessels and nerves in the distal forearm |
Tendons that pass from the forearm into the hand are readily visible in the distal forearm and can be used as landmarks to locate major vessels and nerves.
In the anterior aspect of the distal forearm, the tendons of the flexor carpi radialis, flexor carpi ulnaris, and palmaris longus muscles can be easily located either by palpating or by asking a patient to flex the wrist against resistance.
The tendon of flexor carpi radialis is located approximately at the junction between the lateral and middle thirds of an imaginary line drawn transversely across the distal forearm. The radial artery is immediately lateral to this tendon and this site is used for taking a radial pulse (Fig. 7.122A).
The tendon of the flexor carpi ulnaris is easily palpated along the medial margin of the forearm and inserts on the pisiform, which can also be palpated by following the tendon to the base of the hypothenar eminence of the hand. The ulnar artery and ulnar nerve travel through the distal forearm and into the hand under the lateral lip of the flexor carpi ulnaris tendon and lateral to the pisiform.
The palmaris longus tendon may be absent, but when present, lies medial to the flexor carpi radialis tendon and is particularly prominent when the wrist is flexed against resistance. The median nerve is also medial to the flexor carpi radialis tendon and lies under the palmaris longus tendon.
The long tendons of the digits of the hand are deep to the median nerve and between the long flexors of the wrist. Their position can be visualized by rapidly and repeatedly flexing and extending the fingers from medial to lateral.
In the posterior distal forearm and wrist, the tendons of the extensor digitorum (Fig. 7.122B) are in the midline and radiate into the index, middle, ring, and little fingers from the wrist.
The distal ends of the tendons of the extensor carpi radialis longus and brevis muscles are on the lateral side of the wrist (Fig. 7.122C) and can be accentuated by making a tight fist and extending the wrist against resistance.
The tendon of the extensor carpi ulnaris can be felt on the far medial side of the wrist between the distal end of the ulna and the wrist.
Hyperextension and abduction of the thumb reveals the anatomical snuffbox (Fig. 7.122D). The medial margin of this triangular area is the tendon of the extensor pollicis longus, which swings around the dorsal tubercle of the radius and then travels into the thumb. The lateral margin is formed by the tendons of the extensor pollicis brevis and abductor pollicis longus. The radial artery passes through the anatomical snuffbox when traveling laterally around the wrist to reach the back of the hand and penetrate the base of the first dorsal interosseous muscle to access the deep aspect of the palm of the hand. The pulse of the radial artery can be felt in the floor of the anatomical snuffbox in the relaxed wrist. The cephalic vein crosses the roof of the anatomical snuffbox, and cutaneous branches of the radial nerve can be felt by moving a finger back and forth along the tendon of the extensor pollicis longus muscle.
Normal appearance of the hand
In the resting position, the palm and digits of the hand have a characteristic appearance. The fingers form a flexed arcade, with the little finger flexed the most and the index finger flexed the least (Fig. 7.123A). The pad of the thumb is positioned at a 90° angle to the pads of the fingers.
A thenar eminence occurs at the base of the thumb and is formed by the underlying thenar muscles. A similar hypothenar eminence occurs along the medial margin of the palm at the base of the little finger. The appearance of the thenar and hypothenar eminences, and the positions of the fingers change when the ulnar and median nerves are compromised. |
Major superficial veins of the upper limb begin in the hand from a dorsal venous network (Fig. 7.123B), which overlies the metacarpals. The basilic vein originates from the medial side of the network and the cephalic vein originates from the lateral side.
Position of the flexor retinaculum and the recurrent branch of the median nerve
The proximal margin of the flexor retinaculum can be determined using two bony landmarks.
The pisiform bone is readily palpable at the distal end of the flexor carpi ulnaris tendon.
The tubercle of the scaphoid can be palpated at the distal end of the flexor carpi radialis tendon as it enters the wrist (Fig. 7.124).
An imaginary line between these two points marks the proximal margin of the flexor retinaculum. The distal margin of the flexor retinaculum is approximately deep to the point where the anterior margin of the thenar eminence meets the hypothenar eminence near the base of the palm.
The recurrent branch of the median nerve lies deep to the skin and deep fascia overlying the anterior margin of the thenar eminence near the midline of the palm.
Motor function of the median and ulnar nerves in the hand
The ability to flex the metacarpophalangeal joints while at the same time extending the interphalangeal joints of the fingers is entirely dependent on the intrinsic muscles of the hand (Fig. 7.125A). These muscles are mainly innervated by the deep branch of the ulnar nerve, which carries fibers from spinal cord level (C8)T1.
Adducting the fingers to grasp an object placed between them is caused by the palmar interossei muscles, which are innervated by the deep branch of the ulnar nerve carrying fibers from spinal cord level (C8)T1.
The ability to grasp an object between the pad of the thumb and the pad of one of the fingers depends on normal functioning of the thenar muscles, which are innervated by the recurrent branch of the median nerve carrying fibers from spinal cord level C8(T1).
Visualizing the positions of the superficial and deep palmar arches
The positions of the superficial and deep palmar arches in the hand can be visualized using bony landmarks, muscle eminences, and skin creases (Fig. 7.126).
The superficial palmar arch begins as a continuation of the ulnar artery, which lies lateral to the pisiform bone at the wrist. The arch curves laterally across the palm anterior to the long flexor tendons in the hand. The arch reaches as high as the proximal transverse skin crease of the palm and terminates laterally by joining a vessel of variable size, which crosses the thenar eminence from the radial artery in the distal forearm.
The deep palmar arch originates on the lateral side of the palm deep to the long flexor tendons and between the proximal ends of metacarpals I and II. It arches medially across the palm and terminates by joining the deep branch of the ulnar artery, which passes through the base of the hypothenar muscles and between the pisiform and hook of the hamate. The deep palmar arch is more proximal in the hand than the superficial palmar arch and lies approximately one-half of the distance between the distal wrist crease and the proximal transverse skin crease of the palm.
Peripheral pulses can be felt at six locations in the upper limb (Fig. 7.127).
Axillary pulse: axillary artery in the axilla lateral to the apex of the dome of skin covering the floor of the axilla.
Brachial pulse in midarm: brachial artery on the medial side of the arm in the cleft between the biceps brachii and triceps brachii muscles. This is the position where a blood pressure cuff is placed. |
Brachial pulse in the cubital fossa: brachial artery medial to the tendon of the biceps brachii muscle. This is the position where a stethoscope is placed to hear the pulse of the vessel when taking a blood pressure reading.
Radial pulse in the distal forearm: radial artery immediately lateral to the tendon of the flexor carpi radialis muscle. This is the most common site for “taking a pulse.”
Ulnar pulse in the distal forearm: ulnar artery immediately under the lateral margin of the flexor carpi ulnaris tendon and proximal to the pisiform.
Radial pulse in the anatomical snuffbox: radial artery as it crosses the lateral side of the wrist between the tendon of the extensor pollicis longus muscle and the tendons of the extensor pollicis brevis and abductor pollicis longus muscles.
Fig. 7.1 Upper limb. A. Anterior view of the upper limb. B. Superior view of the shoulder.
Spinous process of vertebra TINeckShoulderGlenohumeral jointArmElbow jointForearmWrist jointHandBAThoracic wallRib IRib IAxillaScapulaManubriumof sternumClavicle
Fig. 7.2 Areas of transition in the upper limb.
Fig. 7.3 Movements of the scapula. A. Rotation. B. Protraction and retraction.
Fig. 7.4 Movements of the arm at the glenohumeral joint.
Fig. 7.5 Movements of the forearm. A. Flexion and extension at the elbow joint. B. Pronation and supination.
Fig. 7.6 Movements of the hand at the wrist joint.
Fig. 7.7 Bones of the upper limb.
Fig. 7.8 Movements of the metacarpophalangeal (A) and interphalangeal (B) joints.
Fig. 7.9 Muscles of the shoulder. A. Posterior shoulder. B. Anterior shoulder. C. Rotator cuff muscles.
SupraspinatusSubscapularisHumerusAcromionSpine of scapulaInfraspinatusTeres minorCoracoid processTrapeziusDeltoidPectoralis majorTeres majorLatissimus dorsiABCTrapeziusLatissimus dorsiLevator scapulaeRhomboid minorRhomboid major
Fig. 7.10 Muscle components in the arm and forearm.
Fig. 7.11 Relationship of the upper limb to the neck.
Axillary arteryAxillary veinAxillaMedial margin ofcoracoid processHumerusAxillary inletSuperior margin of scapulaNerves to upper limbLateral margin of rib I
Fig. 7.12 Muscles of the back and thoracic wall.
Fig. 7.13 Breast.
Fig. 7.14 Innervation of the upper limb.
Anterior ramiNervesMusculocutaneous nerve(C5 to C7)Radial nerve(C5 to C8,T1)Median nerve(C6 to C8,T1)Ulnar nerve(C[7], C8, T1)C5C6C7C8T1Brachial plexus
Fig. 7.15 Dermatomes and myotomes in the upper limb. A. Dermatomes. B. Movements produced by myotomes.
T1T1T1T2T2C6C6C6C5C5C5C4C4C3C3C8C8C8C7C7C7AAbduction of armC5Flexion of elbowC(5)6Adduction and abduction of digitsT1Flexion of digitsC8BC(6)7(8)
Fig. 7.16 Nerves of upper limb. A. Major nerves in the arm and forearm. B. Anterior and posterior areas of skin innervated by major peripheral nerves in the arm and forearm. |
Radial nerve • All muscles in posterior compartment of arm and forearmUlnar nerve• Most intrinsic muscles in hand• Flexor carpi ulnaris and medial half of flexor digitorum profundus in forearmMusculocutaneous nerve• All muscles in anterior compartment of armMedian nerve• Most flexors in forearm• Thenar muscles in handABUlnar nerveMedian nerveRadial nerve• Inferior lateral cutaneous nerve of arm• Posterior cutaneous nerve of arm• Posterior cutaneous nerve of forearmMusculocutaneous nerve• Lateral cutaneous nerve of forearmRadial nerve• Superficial branchPosteriorT1T2Ulnar nerveMedian nerveRadial nerve• Inferior lateral cutaneous nerve of armAxillary nerve• Superior lateral cutaneous nerve of armAxillary nerve• Superior lateral cutaneous nerve of armMusculocutaneous nerve• Lateral cutaneous nerve of forearmRadial nerve• Superficial branchAnteriorT1T2
Fig. 7.17 Nerves related to the humerus.
Radial nerveUlnar nerveAxillary nerveRadial groove of humerusSurgical neck of humerusMedial epicondyle
Fig. 7.18 Veins in the superficial fascia of upper limb. The area of the cubital fossa is shown in yellow.
Clavipectoral triangleClavicleCephalic veinBiceps brachiiAxillary veinCephalic veinPectoralis majorBasilic veinMedian cubital veinDorsal venous network of handBasilic veinCubital fossaDeltoid
Fig. 7.19 A to C. Movements of the thumb.
Fig. 7.20 Right clavicle.
LateralMedialSuperior viewSurface for articulationwith acromionAnterior viewSurface for articulation with manubrium of sternum andfirst costal cartilageTrapezoid lineInferior viewConoid tubercleConoid tubercle
Fig. 7.21 Scapula. A. Posterior view of right scapula. B. Anterior view of costal surface. C. Lateral view.
Articular surface for clavicleCoracoidprocessSuperior borderAnterior view of scapulaSuperior angleMedial borderSubscapular fossaAcromionGlenoid cavityLateral borderInfraglenoid tubercleInferior angleAAcromionSupraglenoid tubercleSuperior angleCoracoid processGlenoid cavityInfraglenoid tubercleInferior angleLateral borderSpinous processLateral viewCMedial borderLateral borderSuperior borderSuperior angleInferior angleArticular surface for clavicleCoracoid processPosterior viewAcromionGlenoid cavityInfraglenoid tubercleSupraspinousfossaSuprascapular notchGreater scapular notch (or spinoglenoid notch)InfraspinousfossaSpine of scapulaB
Fig. 7.22 Proximal end of right humerus.
HeadSuperior facet on greater tubercle(supraspinatus)GreatertubercleIntertubercularsulcusIntertubercularsulcusLesser tubercle(subscapularis)Lateral lip, floor,and medial lip ofintertubercularsulcus (pectoralismajor, latissimusdorsi, and teresmajor, respectively)Deltoid tuberosity(deltoid)Deltoid tuberosity(deltoid)Anatomical neckSurgical neckLateral viewAnterior viewAttachmentfor pectoralis majorAttachment forcoracobrachialisGreatertubercleSuperior facet(supraspinatus)Middle facet(infraspinatus)Inferior facet(teres minor)Surgical neckAnatomicalneckPosterior view
Fig. 7.23 Sternoclavicular joint. A. Bones and ligaments. |
B. Volume-rendered reconstruction using multidetector computed tomography.
CostoclavicularligamentInterclavicularligamentClavicular notchAnteriorsternoclavicularligamentManubrium ofsternumSternal angleArticular disc(capsule and ligamentsremoved anteriorlyto expose joint)Attachment sitefor rib IIFirst costalcartilageRib IVertebral body of TIILeft clavicleSternalangleRib IRib IIManubriumof sternumAB
Fig. 7.24 Right acromioclavicular joint.
Fig. 7.25 Glenohumeral joint. A. Articular surfaces of right glenohumeral joint. B. Radiograph of a normal glenohumeral joint.
Tendon of longhead of bicepsbrachii muscleGlenoid cavityABGlenoid labrumTransverse humeral ligamentClavicleAcromionGlenoid cavityHead of humerusHead ofhumerus
Fig. 7.26 Synovial membrane and joint capsule of right glenohumeral joint.
Synovial sheathSynovial membraneRedundant synovial membrane in adductionSubtendinous bursa of subscapularisLong head of biceps brachii tendonCoracohumeralligamentLong head of biceps brachiitendonFibrous membrane of joint capsule
Fig. 7.27 Capsule of right glenohumeral joint.
Superior glenohumeral ligamentMiddle glenohumeral ligamentInferiorglenohumeralligamentCoracohumeral ligamentTransversehumeral ligamentSynovialsheathTendon oflong headof bicepsbrachiiRedundant capsuleAperture for subtendinousbursa of subscapularis
Fig. 7.28 Lateral view of right glenohumeral joint and surrounding muscles with proximal end of humerus removed.
SupraspinatusInfraspinatusTeres minorTeres majorSynovial membraneSubtendinous bursaof subscapularisLong head of biceps brachii tendonLong head of tricepsbrachiiShort head of biceps brachiiand coracobrachialisLatissimus dorsiPectoralis majorGlenoid labrum Fibrous membraneSubscapularisDeltoidAcromionCoracoid processCoraco-acromial ligamentGlenoid cavitySubacromial bursa (subdeltoid)
Fig. 7.29 Magnetic resonance image (T1-weighted) of a normal glenohumeral joint in the sagittal plane.
SupraspinatusInfraspinatusPosteriorAnteriorClavicleAcromionTeres minorHead of humerusCoracoid processSubscapularis
Fig. 7.30 There is an oblique fracture of the middle third of the right clavicle.
Fracture of clavicleAcromioclavicular joint
Fig. 7.31 Radiographs of acromioclavicular joints. A. Normal right acromioclavicular joint. B. Dislocated right acromioclavicular joint (shoulder separation).
Acromioclavicular jointAcromionClavicle Head of humerusClavicleAcromionHumerusAB
Fig. 7.32 Radiograph showing an anteroinferior dislocation of the shoulder joint.
AcromionGlenoid cavityClavicleHead of humerus
Fig. 7.33 Magnetic resonance image of a full-thickness tear of the supraspinatus tendon as it inserts onto the greater tubercle of the humerus.
Fig. 7.34 Ultrasound of shoulder showing needle placement into the subdeltoid/subacromial bursa.
DeltoidHead of humerusNeedleSubacromial-subdeltoid bursa
Fig. 7.35 Lateral view of trapezius and deltoid muscles.
AcromionSpine of thescapulaTrapeziusDeltoidDeltoid tuberosity of humerusClavicle |
Fig. 7.36 Attachments and neurovascular supply of the trapezius and deltoid muscles.
AcromionSpine of scapulaTrapeziusDeltoidDeltoid tuberosity of humerusRhomboid minorRhomboid majorClavicleSuperior nuchal lineExternal occipitalprotuberanceMastoid processLigamentum nuchaeSpinous processes and interspinous ligaments to TXIIAccessory nerve (XI)Levator scapulaeAxillary nervePosterior circumflex humeral arteryLine of attachment of trapeziusLine of attachment of deltoid
Fig. 7.37 Right posterior scapular region.
Suprascapular notch (foramen) SupraspinatusInfraspinatusCut edge of trapeziusCut edge of deltoidSurgical neck of humerusMedial lip of intertubercular sulcusTriangular intervalTriangular spaceOlecranonLong head of triceps brachiiTeres majorTeres minorQuadrangular spaceCut edge of lateral head of triceps brachii
Fig. 7.38 Arteries and nerves associated with gateways in the posterior scapular region.
Posterior circumflex humeral arteryCircumflex scapular arterySuperior transverse scapular ligamentSuprascapular nerveSuprascapular arteryAxillary nerveProfunda brachii arteryRadial nerveTo deltoidTo skin on lateral part of deltoidCut edge of lateral head of triceps brachii
Fig. 7.39 Arterial anastomoses around the shoulder.
ClaviclePosterior circumflexhumeral arteryAnterior circumflexhumeral arterySubscapular arteryCircumflex scapular arterySuprascapular arteryAxillary arteryProfunda brachii arteryBrachial arteryRight subclavian arteryDeep branch of transversecervical arteryTransverse cervical arteryRib IRight common carotid arteryThyrocervical trunk
Fig. 7.40 Axilla. A. Walls and transition between neck and arm.
Axilla. B. Boundaries. C. Continuity with the arm.
Lateral wallAnterior wallPosterior wallSkinMedial wallCoracoid processAnterior scalene muscleMiddle scalene muscleClavicleLateral margin of rib IA
Axillary sheathsurroundingarteries, veins, nerves, and lymphaticsApex of inletInletAxillaSkin of armSkin on floor of axillaPosterior wall• Subscapularis, teres major, and latissimus dorsi muscles, and long head of triceps brachii muscleLateral wall• Intertubercular sulcusInlet• Lateral margin of rib I• Clavicle• Superior margin of scapula to coracoid processAnterior wall• Pectoralis major and minor muscles• Subclavius muscle• Clavipectoral fasciaMedial wall• Upper thoracic wall • Serratus anterior muscleFloor • Skin of armpit• Opens laterally into armBC
Fig. 7.41 Pectoralis major muscle.
Fig. 7.42 Pectoralis minor and subclavius muscles and clavipectoral fascia.
Pectoralis majorPectoralis majorPectoralis minorClavipectoral fasciaCephalic veinLateral pectoral nerveMedial pectoralnervesPectoral branch of thoraco-acromial arterySubclaviusAttachment of fasciato floor of axilla
Fig. 7.43 Medial wall of the axilla. A. Lateral view. B. Lateral view with lateral angle of scapula retracted posteriorly. C. Anterior view.
IIIIIIIVVVIVIILong thoracic nerveLong thoracic nerveLateral angle ofscapula pulledposterolaterallyaway from thethoracic wallIntercostobrachial nerve (lateral cutaneousbranch of T2)Serratus anteriorSerratus anteriorSerratus anteriorABC |
Fig. 7.44 Lateral wall of the axilla.
Fig. 7.45 Posterior wall of the axilla.
Teres majorLatissimus dorsiLong head of triceps brachiiSubscapularisSuprascapular foramen• Suprascapular nerveTriangular interval • Radial nerve • Profunda brachii arteryTriangular space • Circumflex scapular arteryQuadrangular space • Axillary nerve • Posterior circumflex humeral artery and vein
Fig. 7.46 Magnetic resonance image of the glenohumeral joint in the transverse or horizontal plane.
Glenoid cavityBiceps tendon in intertubercular sulcusSubscapularisGlenoid labrumTeres minor and infraspinatus musclesHead of humerusAnteriorPosterior
Fig. 7.47 Floor of the axilla.
Axillary sheathArmDome of skin onfloor of axillaAnterior axillary skin foldPosterior axillaryskin fold
Fig. 7.48 Contents of the axilla: muscles.
Long head of biceps brachiiShort head of biceps brachiiTendon of biceps brachiiCoracobrachialisBicipital aponeurosisTransverse humeral ligament
Fig. 7.49 Contents of the axilla: the axillary artery.
Lower border of teres majorPectoralis minorLateral margin of rib ISubclaviusSubclavian artery1st part2nd part3rd partBrachial arteryAxillary artery
Fig. 7.50 Branches of the axillary artery.
Posterior circumflex humeral artery(quadrangular space)Anterior circumflex humeral arteryProfunda brachii artery(triangular interval)Long head of triceps brachiiThoraco-acromial arterySubclaviusPectoralis minorSubscapular arterySubscapularisSuperior thoracic arteryLateral thoracic arteryCircumflex scapular branch(triangular space)Thoracodorsal arteryLatissimus dorsiTeres major
Fig. 7.51 Axillary vein.
Fig. 7.52 Brachial plexus. A. Major components in the neck and axilla. B. Schematic showing parts of the brachial plexus.
TerminalnervesCordsDivisionsTrunksRoots(anterior rami)C5C6C7C8T1SuperiorMiddleInferiorLateralPosteriorPosteriorPosteriorPosteriorMedialAnteriorAnteriorAnterior Arrangedaround 2nd part of axillary arteryBSuperior cervical sympathetic ganglionInferior cervical sympathetic ganglionMiddle cervical sympathetic ganglionGray ramuscommunicansRoots (anterior rami of C5 to T1)Trunks (superior, middle, inferior)Divisions (anterior, posterior)Cords (medial, lateral, posterior)C8C7C6C5T1Middle scalene muscleAnterior scalene tendonA
Fig. 7.53 Brachial plexus. A. Schematic showing branches of the brachial plexus. B. Relationships to the axillary artery. |
Terminal nervesCordsDivisionsTrunksRoots (anterior rami)C5C6C7C8T1SuperiorMiddleInferiorLateralPosteriorPosteriorPosteriorPosteriorMedialAnteriorAnteriorAnterior ALateral pectoral nerveMedial pectoral nerveMedial cutaneous nerve of armMedial cutaneous nerve of forearmMusculocutaneousMedianRadialUlnarAxillaryLong thoracicnerveSuprascapular nerveDorsal scapular nerveContribution to phrenic nerveNerve to subclaviusSuperiorsubscapular nerveThoracodorsal nerveInferior subscapular nerveDorsal scapular nerveC5C6C7C8T1T2Suprascapular nerveLateral pectoral nerveMedial cordPosterior cordLateral cordMedial pectoral nerveSecond part of axillary arteryMusculocutaneous nerveAxillary nerveMedian nerveC7 fibersRadial nerveUlnar nerveSuperior subscapular nerveThoracodorsal nerveInferior subscapular nerveMedial cutaneous nerve of armMedial cutaneous nerve of forearmLong thoracic nerveIntercostobrachial nerve (lateral cutaneous branch of T2)Nerve to subclaviusB
Fig. 7.54 Branches of the roots and trunks of the brachial plexus.
Dorsal scapular nerveMiddle scalene muscleAnterior scalene tendonT1 intercostal nerveC5 branch to phrenic nervePhrenic nerveSubclavian veinNerve to subclaviusAxillary arteryLong thoracic nerveSerratus anteriorSuprascapular foramenSuprascapular nerve
Fig. 7.55 Branches of the lateral and medial cords of the brachial plexus.
Lateral pectoral nerveMedial pectoral nerveAxillary arteryMusculocutaneous nerveMedian nerveUlnar nerveLateral cutaneousnerve of armMedial cutaneous nerve of forearmMedial cutaneous nerve of armLateral cordMedial cordPectoralis minorT1 intercostal nerve
Fig. 7.56 Branches of the posterior cord of the brachial plexus.
Axillary nerveSuperior subscapular nerveThoracodorsal nerveInferior subscapular nerveRadial nervePosterior cutaneousnerve of arm
Fig. 7.57 Lymph nodes and vessels in the axilla.
Humeral nodesCentral nodesPectoral nodesApical nodesInfraclavicular nodesSubscapular nodesAnterior scaleneMost of upper limbSome of upper limbAnterolateral body wall and centrolateral part of mammary glandRight subclavian trunkSuperior part of mammary gland
Fig. 7.58 Axillary process of the breast.
Fig. 7.59 Arm. A. Proximal and distal relationships. B. Transverse section through the middle of the arm.
AxillaCubitalfossaLateral intermuscular septumMedial intermuscular septumHumerusAnterior (flexor) compartmentPosterior (extensor) compartmentDeep fasciaForearmABArmLine of section
Fig. 7.60 Humerus. Posterior view.
Fig. 7.61 Distal end of the humerus.
Fig. 7.62 A. Anterior view of the proximal end of the radius. B. Radiograph of the elbow joint (anteroposterior view).
BTrochleaCapitulumLateral epicondyleMedial epicondyleRadiusHead of radiusHumerusUlnaOblique lineHeadRadial tuberosityNeckLateralMedialA
Fig. 7.63 A. Lateral, anterior, medial, and posterior views of the proximal end of the ulna.
B. Radiograph of the elbow joint (lateral view). |
Fig. 7.64 Coracobrachialis, biceps brachii, and brachialis muscles.
Long head of bicepsbrachii muscleShort head of bicepsbrachii muscleCoracobrachialis muscleTransverse humeral ligamentBrachialis muscleTuberosity of ulnaBicipital aponeurosis (cut )Radial tuberosity
Fig. 7.65 Triceps muscle.
OlecranonLong head of triceps brachiiLateral head of triceps brachiiMedial head of triceps brachiiLateral head of triceps brachiiRadial groove of humerus
Fig. 7.66 Brachial artery. A. In context.
Brachial artery. B. Branches.
Fig. 7.67 Veins of the arm.
Axillary veinCoracobrachialisInferior margin of teres majorPaired brachial veinsBasilic veinBrachialisBasilic vein (subcutaneous superficial vein)Basilic vein penetratesdeep fasciaDeep veins accompanying arteriesCephalic veinBiceps brachii
Fig. 7.68 Musculocutaneous, median, and ulnar nerves in the arm.
Median nerveUlnar nerveMedial epicondyleLateral cutaneous nerve of forearmMusculocutaneous nerveMusculocutaneous nerveMedial cordLateral cordRadial nerveMedial intermuscular septum
Fig. 7.69 Radial nerve in the arm.
Ulnar nerveProfunda brachii arteryTriangular intervalInferior lateral cutaneous nerve of armPosterior cutaneous nerve of forearmRadial nerve (in radial groove)Medial epicondyleBranch to medial head of triceps brachii
Fig. 7.70 Radiograph of the humerus demonstrating a midshaft fracture, which may disrupt the radial nerve.
Fig. 7.71 Components and movements of the elbow joint. A. Bones and joint surfaces. B. Flexion and extension. C. Pronation and supination. D. Radiograph of a normal elbow joint (anteroposterior view).
Fig. 7.72 Synovial membrane of elbow joint (anterior view).
Fig. 7.73 Elbow joint. A. Joint capsule and ligaments of the right elbow joint. B. Magnetic resonance image of the elbow joint in the coronal plane.
RadialcollateralligamentAUlnarcollateralligamentAnular ligamentof radiusSacciform recessof synovialmembraneBUlnar collateralligamentRadial collateral ligamentHead of radiusHumerusMedial epicondyleUlna
Fig. 7.74 Radiograph of an elbow showing a fracture of the olecranon and involving the insertion of the triceps brachii muscle.
Fig. 7.75 Radiographs of elbow joint development. A. At age 2 years. B. At age 5 years. C. At age 5–6 years. D. At age 12 years.
Fig. 7.76 MRI of right elbow showing swelling of the ulnar nerve in the cubital tunnel posterior to the medial epicondyle, consistent with nerve compression.
Fig. 7.77 Cubital fossa. A. Margins. B. Contents. C. Position of the radial nerve. D. Superficial structures. |
Ulnar nerveRadial arteryUlnar arteryPronator teres (humeral head)Pronator teres(ulnar head)Median nerveMedian cubitalveinUlnar nerveMedian nerveBasilic veinBasilic veinMedial cutaneousnerve of forearmLateral cutaneousnerve of forearmForearm extensorsLine betweenlateral and medialepicondylesForearm flexorsBrachioradialisBrachialisRadial nerveRadial nerveCephalic veinMusculocutaneous nerveBrachioradialis(pulled back )Deep branchof radial nerveSupinatorSuperficial branch of radial nerveTendon (biceps brachii)Biceps brachiiRadial arteryUlnar arteryTriceps brachiiABCDPronator teres Artery(brachial)Nerve(median)BicipitalaponeurosisMedial intermuscularseptumCubital fossaMedialepicondyleLateralepicondyleTendon (biceps)Artery (brachial)Nerve (median)Ulnar nerveRadial nerve
Fig. 7.78 Digital subtraction angiograms of forearm demonstrating a surgically created radiocephalic fistula.
A. Anteroposterior view. B. Lateral view.
Fig. 7.79 Forearm. A. Proximal and distal relationships of the forearm. B. Transverse section through the middle of the forearm.
Cubital fossaCarpal tunnelUlnaMedian nerveLong flexortendons of digitsBiceps tendonBrachial arteryMedian nerveUlnaRadiusRadiusPosteriorcompartmentDeep fasciaBALateral intermuscular septumAnterior compartmentInterosseous membraneArmElbow jointForearmWrist jointHand
Fig. 7.80 Radius. A. Shaft and distal end of the right radius. B. Radiograph of the forearm (anteroposterior view).
Fig. 7.81 Shaft and distal end of right ulna.
AnteriorsurfaceAnterior border(rounded)Posterior border(sharp)Anterior surfaceInterosseousborderMedialsurfaceAnterior borderPosterior surfaceUlnar styloid processRougheningfor attachmentof pronator quadratusAttachment ofarticular discInterosseousborderTrochlearnotchTuberosity of ulnaCoronoidprocessRadial notchOlecranonAnterior viewDistal view
Fig. 7.82 Distal radio-ulnar joint and the interosseous membrane.
Fig. 7.83 Pronation and supination.
PronatedSupinatedSupinatorBiceps brachiiPronator teresPronator teresand pronatorquadratuscontractSupinator andbiceps brachiicontractPronator quadratusSupinatedAxis of movement
Fig. 7.84 Abduction of the distal end of the ulna by the anconeus during pronation.
Abduction ofulna by anconeusduring pronationAxis of movementwith abduction of ulnaAnconeus
Fig. 7.85 Superficial layer of forearm muscles. A. Superficial muscles (flexor retinaculum not shown). B. Flexor carpi ulnaris muscle.
Median nerveFlexor carpi radialisPalmaris longusFlexor carpi ulnaris Palmar aponeurosisPisometacarpal ligamentPisiformUlnar head offlexor carpi ulnarisABHumeral head ofpronator teresUlnar head ofpronator teresHumeral head offlexor carpi ulnarisUlnar nerveUlnar nerveBrachial arteryUlnar arteryRadial arteryPronator teres (cut )Pisohamate ligamentHook of hamate
Fig. 7.86 Intermediate layer of forearm muscles. |
Median nerveFlexor digitorumsuperficialisUlnar nerve Ulnar arteryFlexor retinaculumHumero-ulnarhead of flexordigitorumsuperficialisUlnar arteryRadial head of flexordigitorumsuperficialisMedian nerve
Fig. 7.87 Deep layer of forearm muscles.
Fig. 7.88 Arteries of the anterior compartment of the forearm.
Fig. 7.89 Nerves of anterior forearm.
Fig. 7.90 Superficial layer of muscles in the posterior compartment of the forearm. A. Brachioradialis muscle (anterior view). B. Superficial muscles (posterior view).
Fig. 7.91 Deep layer of muscles in the posterior compartment of the forearm.
Fig. 7.92 Posterior interosseous artery and radial nerve in posterior compartment of forearm.
Posteriorinterosseous nerve(continuation ofdeep branch ofradial nerve)Commoninterosseous arteryAnteriorinterosseous arteryUlnar arteryPosteriorinterosseous arteryInterosseous membraneSuperficial branchDeep branchRadial nerveBranch tobrachioradialisBranch to extensorcarpi radialis brevisBranch to extensorcarpi radialis longusAnteriorinterosseous arteryPosteriorinterosseous arteryAnterior viewPosterior view
Fig. 7.93 Right hand. The fingers are shown in a normal resting arcade in which they are flexed. In the anatomical position, the digits are straight and adducted.
Carpal bonesThumbLittleRingIndexFingersRadiusWrist jointUlnaProximal skin creaseDistal skin creaseMetacarpalsDigits ofthe handAdductionAdductionAbductionAbductionMiddle
Fig. 7.94 Right hand and wrist joint. A. Bones.
Right hand and wrist joint. B. Radiograph of a normal hand and wrist joint (anteroposterior view). C. Magnetic resonance image of a normal wrist joint in the coronal plane.
RadiusWrist jointIIIIIIIVVScaphoidTrapezoidLunateUlnaTriquetrumTriquetrumPisiformPisiformHook ofhamateHamateHamatePhalangesAMetacarpalsCarpal bonesCapitateCapitateTrapeziumTrapeziumProximalMiddleDistalProximalCarpal bonesCarpal archCarpal archDistalTubercle of trapeziumTrapezoidTubercle of scaphoidTubercle
Fig. 7.95 Deep transverse metacarpal ligaments, right hand.
Fig. 7.96 Wrist radiographs (posteroanterior view). A. Normal. B. Scaphoid fracture.
Fig. 7.97 Radiograph of wrist showing sclerosis in the lunate consistent with avascular necrosis (Kienbock’s disease).
Fig. 7.98 Carpal tunnel. A. Structure and relations. B. Magnetic resonance image of a normal wrist in the axial plane. C. Magnetic resonance image of a normal wrist in the coronal plane.
Fig. 7.99 Palmar aponeurosis, right hand.
Fig. 7.100 Anatomical snuffbox, left hand.
Fig. 7.101 Fibrous digital sheaths and synovial sheaths of the right hand.
Fig. 7.102 MRI of the wrist showing fluid and inflammation associated with the first extensor compartment, consistent with De Quervain’s tenosynovitis.
Fig. 7.103 Extensor hood. A and B. Middle finger, left hand. C. Function of extensor hoods and intrinsic muscles. |
Extensor hoodExtensordigitorum tendonDorsal interosseousmuscleFlexor digitorumprofundus tendonFulcrum ofmetacarpophalangeal jointABCContraction of intrinsicmuscles (lumbricals andinterossei muscles)Deep transversemetacarpal ligamentMiddle fingerFulcrums ofinterphalangeal jointsExtension ofinterphalangeal jointsFlexion ofmetacarpophalangeal jointExtendedFlexedUpstrokePalmar ligamentLumbrical muscle
Fig. 7.104 Dorsal interossei (palmar view), right hand.
Fig. 7.105 Palmar interossei (palmar view), right hand.
AdductionAdductionFirst palmarinterosseous(rudimentary: whenpresent is oftenconsidered part ofeither adductorpollicis or flexorpollicis brevis)Insertion intodorsal expansion
Fig. 7.106 Adductor pollicis, right hand.
Oblique head of adductor pollicisTransverse head of adductor pollicisRadial artery(deep palmar arch)Sesamoid bone
Fig. 7.107 Thenar and hypothenar muscles, right hand.
Flexor retinaculumMedian nerveFlexor carpi ulnarisOpponens digiti minimiAbductor digiti minimiFlexor digiti minimi brevisDeep branch ofulnar artery and nerveRecurrent branch of median nerveAdductor pollicis and first palmarinterosseous insert into medialside of extensor hoodFlexor pollicis brevis and abductorpollicis brevis insert into lateral side of extensor hoodExtensor hoodFlexor pollicis brevisThree thenar musclesThree hypothenar musclesOpponens pollicisAbductor pollicis brevis
Fig. 7.108 Lumbrical muscles, right hand.
Flexor retinaculumFlexor digitorumsuperficialis tendon (cut )Flexor digitorumprofundus tendonAttached to dorsal hoodFirst and second lumbricals(unipennate)Third and fourth lumbricals(bipennate)Flexor pollicislongus tendonDeep transversemetacarpal ligament
Fig. 7.109 Arterial supply of the right hand.
Fig. 7.110 Superficial palmar arch, right hand.
Fig. 7.111 Deep palmar arch, right hand.
Radial arteryUlnar arteryUlnar nerveDeep branchof ulnar arteryPerforatingarteryPalmarmetacarpalarteriesDeep palmar archAdductorpollicismuscleRadialis indicisarteryPrincepspollicis arteryFirst dorsalinterosseous muscleFirst dorsalmetacarpalarteryMainly radial arteryDorsalmetacarpalarteriesDorsal carpalnetworkDorsalcarpal archDorsaldigitalarteriesDorsalcarpal branchof ulnar arteryPosteriorinterosseousarteryDorsal viewarcharteryExtensordigitorumtendons(cut)DorsalmetacarpalarteriesFirst dorsalmetacarpalarteryDorsal carpalDorsal carpalbranch of ulnarExtensor pollicis brevisAbductor pollicis longusExtensor pollicis longusExtensor retinaculumExtensor carpiradialis longusRadial artery inanatomical snuffboxExtensor carpiradialis brevisDorsal interosseiDorsal digitalarteriesDorsal branches of properpalmar digital arteries
Fig. 7.112 Dorsal venous arch of the right hand.
Fig. 7.113 Ulnar nerve in the right hand. |
Palmar viewDorsal viewMedial twolumbricalmusclesPalmar branch of ulnarnerve from forearmArea of distribution ofsuperficial branch of ulnarnerve in handDorsal branch of ulnarnerve from forearmUlnar nerveDeep branch(of ulnar nerve)Superficial branch(of ulnar nerve)Ulnar artery
Fig. 7.114 Typical appearance of a “clawed hand” due to a lesion of the ulnar nerve.
Fig. 7.115 Median nerve in the right hand.
Recurrent branch(of median nerve)Lateral twolumbrical musclesPalmar branch of mediannerve from forearmDigital nervesMedian nervePalmar branch(of median nerve)Abductor pollicis brevisFlexor pollicis brevisPalmar viewDorsal view
Fig. 7.116 Radial nerve in the right hand.
Fig. 7.117 Bony landmarks and muscles of the posterior scapular region. Posterior view of shoulder and back.
Teres major muscleTrapezius muscleDeltoid muscleAxillary nerveLatissimus dorsi muscleSpine of scapulaAcromionSupraspinatus muscleInfraspinatus muscleTeres minor musclePosterior axillary skin fold
Fig. 7.118 Visualizing the axilla and locating its contents and related structures. A. Anterior shoulder showing folds and walls of the axilla.
B. Anterior shoulder showing outlet and floor of the axilla. C. Anterior view showing the axillary neurovascular bundle and long thoracic nerve. D. Anterior view of the shoulder showing the clavipectoral triangle with the cephalic vein.
ClavicleCoracoid processHumerusAnterior axillaryskin foldAnterior wallPosterior wallMedial wallLateral wallNeurovascular bundleSerratus anteriormuscleLong thoracic nerveAxillaDeltoid musclePectoralis major muscleCephalic veinClavipectoral triangleFloor of axillaOpening ofaxilla into armAnterior axillary skin foldPosterioraxillary skin foldABCD
Fig. 7.119 Locating the brachial artery in the right arm (medial view of arm with brachial artery, median nerve, and ulnar nerve).
Fig. 7.120 Triceps brachii tendon and position of the radial nerve (posterior view of right arm).
Fig. 7.121 Cubital fossa (anterior view, right arm). A. Anterior view. B. Boundaries and contents. C. Showing radial and ulnar nerves, and veins.
Fig. 7.122 Identifying tendons and locating major vessels and nerves in the distal right forearm. A. Anterior distal forearm and wrist. B. Posterior distal forearm and wrist. C. Lateral view of posterior wrist and forearm. D. Anatomical snuffbox.
Fig. 7.123 Normal appearances of the right hand. A. Palmar view with the thenar and hypothenar eminences and finger arcade. B. Dorsal view with dorsal venous network.
Fig. 7.124 Anterior view of left hand to show the position of the flexor retinaculum and recurrent branch of the median nerve.
Recurrent branch of the median nervePisiform Tubercle ofthe scaphoidFlexor carpiradialis tendonMedian nerveFlexor carpiulnaris tendonFlexor retinaculumHypothenar eminenceThenar eminence
Fig. 7.125 Motor function of the ulnar and median nerves in the hand. A. Flexing the metacarpophalangeal joints and extending the interphalangeal joints: the “ta-ta” position. B. Grasping an object between the fingers. C. Grasping an object between the pad of the thumb and pad of the index finger. |
Fig. 7.126 Visualizing the positions of the superficial and deep palmar arches, left hand. The proximal transverse skin crease of the palm and distal wrist crease are labeled and the superficial and deep palmar arches shown in overlay. This also shows the position of the pisiform and the hook of the hamate.
Distal transverseskin crease of palmPisiform Distal wrist creaseProximal transverseskin crease of palmProximalwrist creaseUlnar arteryRadial arteryHook of hamateDeep palmar archSuperficial palmar arch
Fig. 7.127 Where to take peripheral artery pulses in the upper limb. A. Pulse points. B. Placement of blood pressure cuff and stethoscope.
ABBrachial pulse in midarmBrachial pulse in the cubital fossaUlnar pulse in distal forearmRadial pulse in the anatomical snuffboxRadial pulse in distal forearmAxillary pulse eFig. 7.128 Ultrasound showing a completely torn supraspinatus tendon with fluid in the subacromial subdeltoid bursa.
Deltoid muscleTear in supraspinatus tendonNormal supraspinatus tendonHead of humerusHead of humerus eFig. 7.129 The radiograph, anteroposterior view, demonstrates an anteroinferior dislocation of the humeral head at the glenohumeral joint.
Table 7.1 Muscles of the shoulder (spinal segments in bold are the major segments innervating the muscle)
Table 7.2 Muscles of the posterior scapular region (spinal segments in bold are the major segments innervating the muscle)
Table 7.3 Muscles of the anterior wall of the axilla (spinal segments in bold are the major segments innervating the muscle)
Table 7.4 Muscle of the medial wall of the axilla (spinal segment in bold is the major segment innervating the muscle)
Table 7.5 Muscles of the lateral and posterior wall of the axilla (spinal segments in bold are the major segments innervating the muscle; spinal segments in parentheses do not consistently innervate the muscle)
Table 7.6 Muscles having parts that pass through the axilla (spinal segments in bold are the major segments innervating the muscle)
Table 7.7 Branches of brachial plexus (parentheses indicate that a spinal segment is a minor component of the nerve or is inconsistently present in the nerve)
Table 7.8 Muscles of the anterior compartment of the arm (spinal segments in bold are the major segments innervating the muscle)
Table 7.9 Muscle of the posterior compartment of the arm (spinal segment indicated in bold is the major segment innervating the muscle)
Table 7.10 Superficial layer of muscles in the anterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
Table 7.11 Intermediate layer of muscles in the anterior compartment of the forearm (spinal segment indicated in bold is the major segment innervating the muscle)
Table 7.12 Deep layer of muscles in the anterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
Table 7.13 Superficial layer of muscles in the posterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
Table 7.14 Deep layer of muscles in the posterior compartment of the forearm (spinal segments indicated in bold are the major segments innervating the muscle)
Table 7.15 Intrinsic muscles of the hand (spinal segments indicated in bold are the major segments innervating the muscle)
In the clinic
Fracture of the proximal humerus |
It is extremely rare for fractures to occur across the anatomical neck of the humerus because the obliquity of such a fracture would have to traverse the thickest region of bone. Typically fractures occur around the surgical neck of the humerus. Although the axillary nerve and posterior circumflex humeral artery may be damaged with this type of fracture, this rarely happens. It is important that the axillary nerve is tested before relocation to be sure that the injury has not damaged the nerve and that the treatment itself does not cause a neurological deficit.
In the clinic
Fractures of the clavicle and dislocations of the acromioclavicular and sternoclavicular joints
The clavicle provides the only bony connection between the upper limb and trunk. Given its relative size and the potential forces that it transmits from the upper limb to the trunk, it is not surprising that it is often fractured. The typical site of fracture is the middle third (Fig. 7.30). The medial and lateral thirds are rarely fractured.
The acromial end of the clavicle tends to dislocate at the acromioclavicular joint with trauma (Fig. 7.31). The outer third of the clavicle is joined to the scapula by the conoid and trapezoid ligaments of the coracoclavicular ligament.
A minor injury tends to tear the fibrous joint capsule and ligaments of the acromioclavicular joint, resulting in acromioclavicular separation on a plain radiograph. More severe trauma will disrupt the conoid and trapezoid ligaments of the coracoclavicular ligament, which results in elevation and upward subluxation of the clavicle.
The typical injury at the medial end of the clavicle is an anterior or posterior dislocation of the sternoclavicular joint. Importantly, a posterior dislocation of the clavicle may impinge on the great vessels in the root of the neck and compress or disrupt them.
In the clinic
Dislocations of the glenohumeral joint
The glenohumeral joint is extremely mobile, providing a wide range of movement at the expense of stability. The relatively small bony glenoid cavity, supplemented by the less robust fibrocartilaginous glenoid labrum and the ligamentous support, make it susceptible to dislocation.
Anterior dislocation (Fig. 7.32) occurs most frequently and is usually associated with an isolated traumatic incident (clinically, all anterior dislocations are anteroinferior). In some cases, the anteroinferior glenoid labrum is torn with or without a small bony fragment. Once the joint capsule and cartilage are disrupted, the joint is susceptible to further (recurrent) dislocations. When an anteroinferior dislocation occurs, the axillary nerve may be injured by direct compression of the humeral head on the nerve inferiorly as it passes through the quadrangular space. Furthermore, the “lengthening” effect of the humerus may stretch the radial nerve, which is tightly bound within the radial groove, and produce a radial nerve paralysis. Occasionally, an anteroinferior dislocation is associated with a fracture, which may require surgical reduction.
Posterior dislocation is extremely rare; when seen, the clinician should focus on its cause, the most common being extremely vigorous muscle contractions, which may be associated with an epileptic seizure caused by electrocution. Treatment of recurrent instability can be challenging. The aims of treatment are to maintain function and range of movement while preventing instability (subluxation, dislocation, and the “feeling” of dislocation). This can be achieved through physical therapy and shoulder “re-education.” If this fails, capsular tightening and stabilization of the labrum can be achieved arthroscopically. If the problem persists, the coracoid process can be divided at the base, maintaining continuity of the muscular attachments. The process is transferred and a screw fixed to the anterior inferior border of the glenoid to form a buttress to prevent future dislocations.
In the clinic |
The two main disorders of the rotator cuff are impingement and tendinopathy. The muscle most commonly involved is supraspinatus as it passes beneath the acromion and the acromioclavicular ligament. This space, beneath which the supraspinatus tendon passes, is of fixed dimensions. Swelling of the supraspinatus muscle, excessive fluid within the subacromial/subdeltoid bursa, or subacromial bony spurs may produce significant impingement when the arm is abducted.
The blood supply to the supraspinatus tendon is relatively poor. Repeated trauma, in certain circumstances, makes the tendon susceptible to degenerative change, which may result in calcium deposition, producing extreme pain. The calcium deposits can be extracted through a needle under image guidance and often have the consistency of toothpaste.
When the supraspinatus tendon has undergone significant degenerative change, it is more susceptible to trauma, and partialor full-thickness tears may develop (Fig. 7.33). These tears are most common in older patients and may result in considerable difficulty in carrying out normal activities of daily living such as combing hair. However, complete tears may be entirely asymptomatic.
In the clinic
Inflammation of the subacromial (subdeltoid) bursa
Between the supraspinatus and deltoid muscles laterally and the acromion medially, there is a bursa referred to clinically as the subacromial or subdeltoid bursa. In patients who have injured the shoulder or who have supraspinatus tendinopathy, this bursa may become inflamed, making movements of the glenohumeral joint painful. These inflammatory changes may be treated by injection of a corticosteroid and local anesthetic agent (Fig. 7.34).
In the clinic
Hypertrophy of the quadrangular space muscles or fibrosis of the muscle edges may impinge on the axillary nerve. Uncommonly, this produces weakness of the deltoid muscle. Typically it produces atrophy of the teres minor muscle, which may affect the control that the rotator cuff muscles exert on shoulder movement.
In the clinic ”Winging” of the scapula
Because the long thoracic nerve passes down the lateral thoracic wall on the external surface of the serratus anterior muscle, just deep to skin and subcutaneous fascia, it is vulnerable to damage. Loss of function of this muscle causes the medial border, and particularly the inferior angle, of the scapula to elevate away from the thoracic wall, resulting in characteristic “winging” of the scapula, on pushing forward with the arm. Furthermore, normal elevation at the arm is no longer possible.
In the clinic
Imaging the blood supply to the upper limb
When there is clinical evidence of vascular compromise to the upper limb, or vessels are needed to form an arteriovenous fistula (which is necessary for renal dialysis), imaging is required to assess the vessels.
Ultrasound is a useful tool for carrying out a noninvasive assessment of the vessels of the upper limb from the third part of the subclavian artery to the deep and superficial palmar arteries. Blood flow can be quantified and anatomical variants can be noted.
Angiography is carried out in certain cases. The femoral artery is punctured below the inguinal ligament and a long catheter is placed through the iliac arteries and around the arch of the aorta to enter either the left subclavian artery or the brachiocephalic trunk and then the right subclavian artery. Radiopaque contrast agents are injected into the vessel and radiographs are obtained as the contrast agents pass first through the arteries, then the capillaries, and finally the veins.
In the clinic
Trauma to the arteries of the upper limb
The arterial supply to the upper limb is particularly susceptible to trauma in places where it is relatively fixed or in a subcutaneous position.
Fracture of rib I |
As the subclavian artery passes out of the neck and into the axilla, it is fixed in position by the surrounding muscles to the superior surface of rib I. A rapid deceleration injury involving upper thoracic trauma may cause a first rib fracture, which may significantly compromise the distal part of the subclavian artery or the first part of the axillary artery. Fortunately, there are anastomotic connections between branches of the subclavian artery and the axillary artery, which form a network around the scapula and proximal end of the humerus; therefore, even with complete vessel transection, the arm is rarely rendered completely ischemic (ischemia is poor blood supply to an organ or a limb).
Anterior dislocation of the humeral head
Anterior dislocation of the humeral head may compress the axillary artery, resulting in vessel occlusion. This is unlikely to render the upper limb completely ischemic, but it may be necessary to surgically reconstruct the axillary artery to obtain pain-free function. Importantly, the axillary artery is intimately related to the brachial plexus, which may be damaged at the time of anterior dislocation.
In the clinic
There are a number of routes through which central venous access may be obtained. The “subclavian route” and the jugular routes are commonly used by clinicians. The subclavian route is a misnomer that remains the preferred term in clinical practice. In fact, most clinicians enter the first part of the axillary vein.
There are a number of patients that undergo catheterization of the subclavian vein/axillary vein. Entering the subclavian vein/axillary vein is a relatively straightforward technique. The clavicle is identified and a sharp needle is placed in the infraclavicular region, aiming superomedially. When venous blood is aspirated, access has been obtained. This route is popular for long-term venous access, such as Hickman lines, and for shorter-term access where multiple-lumen catheters are inserted (e.g., intensive care unit).
The subclavian vein/axillary vein is also the preferred site for insertion of pacemaker wires. There is, however, a preferred point of entry into the vein to prevent complications. The vein should be punctured in the midclavicular line or lateral to this line. The reason for this puncture site is the course of the vein and its relationship to other structures. The vein passes anterior to the artery, superior to the first rib, and inferior to the clavicle as it courses toward the thoracic inlet. Beneath the clavicle is situated the subclavius muscle. Should the puncture of the vein enter where the subclavius muscle is related to the axillary vein, the catheter or wire may become kinked at this point. Moreover, the constant contraction and relaxation of this muscle will induce fatigue in the line and wire, which may ultimately lead to fracture. A fractured pacemaker wire or a rupture in a chemotherapy catheter can have severe consequences for the patient.
In the clinic
Injuries to the brachial plexus
The brachial plexus is an extremely complex structure. When damaged, it requires meticulous clinical history taking and examination. Assessment of the individual nerve functions can be obtained by nerve conduction studies and electromyography, which assess the latency of muscle contraction when the nerve is artificially stimulated.
Brachial plexus injuries are usually the result of blunt trauma producing nerve avulsions and disruption. These injuries are usually devastating for the function of the upper limb and require many months of dedicated rehabilitation for even a small amount of function to return.
Spinal cord injuries in the cervical region and direct pulling injuries tend to affect the roots of the brachial plexus. Severe trauma to the first rib usually affects the trunks. The divisions and cords of the brachial plexus can be injured by dislocation of the glenohumeral joint.
In the clinic |
Lymphatic drainage from the lateral part of the breast passes through nodes in the axilla. Significant disruption to the normal lymphatic drainage of the upper limb may occur if a mastectomy or a surgical axillary nodal clearance has been carried out for breast cancer. Furthermore, some patients have radiotherapy to the axilla to prevent the spread of metastatic disease, but a side effect of this is the destruction of the tiny lymphatics as well as the cancer cells.
If the lymphatic drainage of the upper limb is damaged, the arm may swell and pitting edema (lymphedema) may develop.
In the clinic
Rupture of biceps tendon
It is relatively unusual for muscles and their tendons to rupture in the upper limb; however, the tendon that most commonly ruptures is the tendon of the long head of the biceps brachii muscle. In isolation, this has relatively little effect on the upper limb, but it does produce a characteristic deformity—on flexing the elbow, there is an extremely prominent bulge of the muscle belly as its unrestrained fibers contract—the “Popeye” sign.
Distal biceps tendon rupture also occurs. It is important to determine the site of the rupture, whether it’s at the musculotendinous junction, midtendon, or at the insertion because this will determine the surgical approach for repair.
In the clinic
Blood pressure measurement is an extremely important physiological parameter. High blood pressure (hypertension) requires treatment to prevent long-term complications such as stroke. Low blood pressure may be caused by extreme blood loss, widespread infection, or poor cardiac output (e.g., after myocardial infarction). Accurate measurement of blood pressure is essential.
Most clinicians use a sphygmomanometer and a stethoscope. The sphygmomanometer is a device that inflates a cuff around the midportion of the arm to compress the brachial artery against the humerus. The cuff is inflated so it exceeds the systolic blood pressure (greater than 120 mm Hg). The clinician places a stethoscope over the brachial artery in the cubital fossa and listens (auscultates) for the pulse. As the pressure in the arm cuff of the sphygmomanometer is reduced just below the level of the systolic blood pressure, the pulse becomes audible as a regular thumping sound. As the pressure in the sphygmomanometer continues to drop, the regular thumping sound becomes clearer. When the pressure in the sphygmomanometer is less than that of the diastolic blood pressure, the audible thumping sound becomes inaudible. Using the simple scale on the sphygmomanometer, the patient’s blood pressure can be determined. The normal range is 90–120/60–80 mm Hg (systolic blood pressure/diastolic blood pressure).
In the clinic
Radial nerve injury in the arm
The radial nerve is tightly bound with the profunda brachii artery between the medial and lateral heads of the triceps brachii muscle in the radial groove. If the humerus is fractured, the radial nerve may become stretched or transected in this region, leading to permanent damage and loss of function. This injury is typical (Fig. 7.70) and the nerve should always be tested when a fracture of the midshaft of the humerus is suspected. The patient’s symptoms usually include wrist drop (due to denervation of the extensor muscles) and sensory changes over the dorsum of the hand.
In the clinic
Median nerve injury in the arm
In the arm and forearm the median nerve is usually not injured by trauma because of its relatively deep position. The commonest neurological problem associated with the median nerve is compression beneath the flexor retinaculum at the wrist (carpal tunnel syndrome). |
On very rare occasions, a fibrous band may arise from the anterior aspect of the humerus beneath which the median nerve passes. This is an embryological remnant of the coracobrachialis muscle and is sometimes called the ligament of Struthers; occasionally, it may calcify. This band can compress the median nerve, resulting in weakness of the flexor muscles in the forearm and the thenar muscles. Nerve conduction studies will demonstrate the site of nerve compression.
In the clinic
Supracondylar fracture of the humerus
Elbow injuries in children may result in a transverse fracture of the distal end of the humerus, above the level of the epicondyles. This fracture is termed a supracondylar fracture. The distal fragment and its soft tissues are pulled posteriorly by the triceps muscle. This posterior displacement effectively “bowstrings” the brachial artery over the irregular proximal fracture fragment. In children, this is a relatively devastating injury: the muscles of the anterior compartment of the forearm are rendered ischemic and form severe contractions, significantly reducing the function of the anterior compartment and flexor muscles (Volkmann’s ischemic contracture).
In the clinic
Pulled elbow is a disorder that typically occurs in children under 5 years of age. It is commonly caused by a sharp pull of the child’s hand, usually when the child is pulled up a curb. The not-yet-developed head of the radius and the laxity of the anular ligament of the radius allow the head to sublux from this cuff of tissue. Pulled elbow is extremely painful, but can be treated easily by simple supination and compression of the elbow joint by the clinician. When the radial head is relocated the pain subsides immediately and the child can continue with normal activity.
In the clinic
Fracture of the olecranon
Fractures of the olecranon can result from a direct blow to the olecranon or from a fall onto an outstretched hand (Fig. 7.74). The triceps inserts into the olecranon and injuries can cause avulsion of the muscle.
In the clinic
Developmental changes in the elbow joint
The elbow joint can be injured in many ways; the types of injuries are age dependent. When a fracture or soft tissue trauma is suspected, a plain lateral and an anteroposterior radiograph are obtained. In an adult it is usually not difficult to interpret the radiograph, but in children additional factors require interpretation.
As the elbow develops in children, numerous secondary ossification centers appear before and around puberty. It is easy to mistakenly interpret these as fractures. In addition, it is also possible for the epiphyses and apophyses to be “pulled off” or disrupted. Therefore, when interpreting a child’s radiograph of the elbow, the physician must know the child’s age (Fig. 7.75). Fusion occurs at around the time of puberty. An understanding of the normal epiphyses and apophyses and their normal relationship to the bones will secure a correct diagnosis. The approximate ages of appearance of the secondary ossification centers around the elbow joint are: capitulum—1 year, head (of radius)—5 years, medial epicondyle—5 years, trochlea—11 years, olecranon—12 years, and lateral epicondyle—13 years.
In the clinic
Fracture of the head of the radius
A fracture of the head of the radius is a common injury and can cause appreciable morbidity. It is one of the typical injuries that occur with a fall on the outstretched hand. On falling, the force is transmitted to the radial head, which fractures. These fractures typically result in loss of full extension, and potential surgical reconstruction may require long periods of physiotherapy to obtain a full range of movement at the elbow joint. |
A lateral radiograph of a fracture of the head of the radius typically demonstrates the secondary phenomenon of this injury. When the bone is fractured, fluid fills the synovial cavity, elevating the small pad of fat within the coronoid and olecranon fossae. These fat pads appear as areas of lucency on the lateral radiograph—the “fat pad” sign. This radiological finding is useful because fracture of the head of the radius is not always clearly visible. If there is an appropriate clinical history, tenderness around the head of the radius, and a positive fat pad sign, a fracture can be inferred clinically even if no fracture can be identified on the radiograph, and appropriate treatment can be instituted.
In the clinic
It is not uncommon for people who are involved in sports such as golf and tennis to develop an overuse strain of the origins of the flexor and extensor muscles of the forearm. The pain is typically around the epicondyles and usually resolves after rest and physical therapy. It may also be treated with injection of the patient’s own plasma, rich in platelets, into the tendon to promote tendon healing and repair. If pain and inflammation persist, surgical division of the extensor or flexor origin from the bone may be necessary. Typically, in tennis players this pain occurs on the lateral epicondyle and common extensor origin (tennis elbow), whereas in golfers it occurs on the medial epicondyle and common flexor origin.
In the clinic
Osteoarthritis is extremely common and is usually most severe in the dominant limb. From time to time an arthritic elbow may undergo such degenerative change that small bone fragments appear in the articular cavity. Given the relatively small joint space, these fragments can result in an appreciable reduction in flexion and extension, and typically lodge within the olecranon and coronoid fossae.
In the clinic
Ulnar nerve injury at the elbow
Posterior to the medial epicondyle of the humerus the ulnar nerve is bound in a fibro-osseous tunnel (the cubital tunnel) by a retinaculum. Older patients may develop degenerative changes within this tunnel, which compresses the ulnar nerve when flexed. The repeated action of flexion and extension of the elbow may cause local nerve damage, resulting in impaired function of the ulnar nerve. Accessory muscles and localized neuritis in this region secondary to direct trauma may also produce ulnar nerve damage (Fig. 7.76).
In the clinic
Construction of a dialysis fistula
Many patients throughout the world require renal dialysis for kidney failure. The patient’s blood is filtered and cleaned by the dialysis machine. Blood therefore has to be taken from patients into the filtering device and then returned to them. This process of dialysis occurs over many hours and requires considerable flow rates of 250–500 mL per minute. To enable such large volumes of blood to be removed from and returned to the body, the blood is taken from vessels that have a high flow. As no veins in the peripheral limbs have such high flow, a surgical procedure is necessary to create such a system. In most patients, the radial artery is anastomosed (joined) to the cephalic vein (Fig. 7.78) at the wrist, or the brachial artery is anastomosed to the cephalic vein at the elbow. Some surgeons place an arterial graft between these vessels.
After six weeks, the veins increase in size in response to their arterial blood flow and are amenable to direct cannulation or dialysis.
In the clinic
Fractures of the radius and ulna
The radius and ulna are attached to the humerus proximally and the carpal bones distally by a complex series of ligaments. Although the bones are separate, they behave as one. When a severe injury occurs to the forearm it usually involves both bones, resulting in either fracture of both bones or more commonly a fracture of one bone and a dislocation of the other. Commonly, the mechanism of injury and the age of the patient determine which of these are likely to occur.
There are three classic injuries to the radius and ulna: |
Monteggia’s fracture is a fracture of the proximal third of the ulna and an anterior dislocation of the head of the radius at the elbow.
Galeazzi’s fracture is a fracture of the distal third of the radius associated with subluxation (partial dislocation) of the head of the ulna at the wrist joint.
Colles’ fracture is a fracture, and posterior displacement, of the distal end of the radius.
Whenever a fracture of the radius or ulna is demonstrated radiographically, further images of the elbow and wrist should be obtained to exclude dislocations.
In the clinic
Transection of the radial or ulnar artery
Adult patients may transect the radial or ulnar artery because these vessels are relatively subcutaneous. A typical method of injury is when the hand is forced through a plate glass window. Fortunately, the dual supply to the hand usually enables the surgeon to tie off either the ulnar or the radial artery, without significant consequence.
In the clinic
Fracture of the scaphoid and avascular necrosis of the proximal scaphoid
The commonest carpal injury is a fracture across the waist of the scaphoid bone (Fig. 7.96). It is uncommon to see other injuries. In approximately 10% of individuals, the scaphoid bone has a sole blood supply from the radial artery, which enters through the distal portion of the bone to supply the proximal portion. When a fracture occurs across the waist of the scaphoid, the proximal portion therefore undergoes avascular necrosis. It is impossible to predict which patients have this blood supply.
In the clinic
Interruption of the blood supply to the lunate can lead to avascular necrosis of the lunate, known as Kienbock’s disease (Fig. 7.97). This can cause pain and stiffness and arthritis in the longer term.
In the clinic
A large median artery is an anatomical variant found in some individuals, where a persistent artery runs alongside the median nerve in one or both forearms and through the carpal tunnel. Individuals are at risk from heavy bleeding from deep cuts to the wrist.
In the clinic
Carpal tunnel syndrome is an entrapment syndrome caused by pressure on the median nerve within the carpal tunnel. The etiology of this condition is often obscure, though in some instances the nerve injury may be a direct effect of increased pressure on the median nerve caused by overuse, swelling of the tendons and tendon sheaths (e.g., rheumatoid arthritis), and cysts arising from the carpal joints. Increased pressure in the carpal tunnel is thought to cause venous congestion that produces nerve edema and anoxic damage to the capillary endothelium of the median nerve itself.
Patients typically report pain and pins-and-needles sensations in the distribution of the median nerve. Weakness and loss of muscle bulk of the thenar muscles may also occur. Gently tapping over the median nerve (in the region of the flexor retinaculum) readily produces these symptoms (Tinel’s sign).
Initial treatment is aimed at reducing the inflammation and removing any repetitive insults that produce the symptoms. If this does not lead to improvement, nerve conduction studies will be necessary to confirm nerve entrapment, which may require surgical decompression of the flexor retinaculum.
In the clinic
The palmar fascia can become abnormally thickened in certain individuals, causing the fingers to progressively develop a fixed flexion position. This results in loss of dexterity and function, and in severe cases requires surgical removal of the abnormal tissue.
In the clinic
The anatomical snuffbox is an important clinical region. When the hand is in ulnar deviation, the scaphoid becomes palpable within the snuffbox. This position enables the physician to palpate the bone to assess for a fracture. The pulse of the radial artery can also be felt in the snuffbox.
In the clinic |
De Quervain’s syndrome is an inflammatory disorder that occurs within the first dorsal extensor compartment and involves the extensor pollicis brevis tendon and abductor pollicis longus tendon and their common tendon sheath (Fig. 7.102). Patients typically present with significant wrist pain preventing appropriate flexion/extension and abduction of the thumb. The cause of this disorder is often overuse. For example, the syndrome is common in young mothers who are constantly lifting young children. Other causes include inflammatory disorders such as rheumatoid arthritis.
In the clinic
Tenosynovitis is inflammation of a tendon and its sheath. The condition may be caused by overuse; however, it can also be associated with other disorders such as rheumatoid arthritis and connective tissue pathologies. If the inflammation becomes severe and ensuing fibrosis occurs, the tendon will not run smoothly within the tendon sheath, and typically within the fingers the tendon may stick or require excess force to fully extend and flex, producing a “triggering” phenomenon.
In the clinic
Trigger finger is a common disorder of late childhood and adulthood and is typically characterized by catching or snapping and occasionally locking of the flexor tendon(s) in the hand. Trigger finger can be associated with significant dysfunction and pain. The triggering is usually related to fibrosis and tightening of the flexor tendon sheath at the level of the metacarpophalangeal joint.
In the clinic
To test for adequate anastomoses between the radial and ulnar arteries, compress both the radial and ulnar arteries at the wrist, then release pressure from one or the other, and determine the filling pattern of the hand. If there is little connection between the deep and superficial palmar arteries, only the thumb and lateral side of the index finger will fill with blood (become red) when pressure on the radial artery alone is released.
In the clinic
In many patients, venous access is necessary for obtaining blood for laboratory testing and administering fluid and intravenous drugs. The ideal sites for venous access are typically in the cubital fossa and in the cephalic vein adjacent to the anatomical snuffbox. The veins are simply distended by use of a tourniquet. A tourniquet should be applied enough to allow the veins to become prominent. For straightforward blood tests the antecubital vein is usually the preferred site, and although it may not always be visible, it is easily palpated. The cephalic vein is generally the preferred site for a short-term intravenous cannula.
In the clinic
The ulnar nerve is most commonly injured at two sites: the elbow and the wrist.
At the elbow, the nerve lies posterior to the medial epicondyle.
At the wrist, the ulnar nerve passes superficial to the flexor retinaculum and lies lateral to the pisiform bone.
Ulnar nerve lesions are characterized by “clawing” of the hand, in which the metacarpophalangeal joints of the fingers are hyperextended and the interphalangeal joints are flexed because the function of most of the intrinsic muscles of the hand is lost (Fig. 7.114).
Clawing is most pronounced in the medial fingers because the function of all intrinsic muscles of these digits is lost while in the lateral two digits, the lumbricals are innervated by the median nerve. Function of the adductor pollicis muscle is also lost.
In lesions of the ulnar nerve at the elbow, function of the flexor carpi ulnaris muscle and flexor digitorum profundus to the medial two digits is lost as well. Clawing of the hand, particularly of the little and ring fingers, is worse with lesions of the ulnar nerve at the wrist than at the elbow because interruption of the nerve at the elbow paralyzes the ulnar half of the flexor digitorum profundus, which leads to lack of flexion at the distal interphalangeal joints in these fingers. |
Ulnar nerve lesions at the elbow and wrist result in impaired sensory innervation on the palmar aspect of the medial one and one-half digits.
Damage to the ulnar nerve at the wrist or at a site proximal to the wrist can be distinguished by evaluating the status of function of the dorsal branch (cutaneous) of the ulnar nerve, which originates in distal regions of the forearm. This branch innervates skin over the dorsal surface of the hand on the medial side.
In the clinic
Around the elbow joint the radial nerve divides into its two terminal branches—the superficial branch and the deep branch.
The most common radial nerve injury is damage to the nerve in the radial groove of the humerus, which produces a global paralysis of the muscles of the posterior compartment, resulting in wrist drop. Radial nerve damage can result from fracture of the shaft of the humerus as the radial nerve spirals around in the radial groove. The typical injury produces reduction of sensation in the cutaneous distribution, predominantly over the posterior aspect of the hand. Severing the posterior interosseous nerve (continuation of deep branch of radial nerve) may paralyze the muscles of the posterior compartment of the forearm, but the nerve supply is variable. Typically, the patient may not be able to extend the fingers.
The distal branches of the superficial branch of the radial nerve can be readily palpated as “cords” passing over the tendon of the extensor pollicis longus in the anatomical snuffbox. Damage to these branches is of little consequence because they supply only a small area of skin.
A 57-year-old woman underwent a right mastectomy for a breast cancer. The surgical note reported that all of the breast tissue had been removed, including the axillary process. In addition, the surgeon had dissected all lymph nodes within the axilla with their surrounding fat. The patient made an uneventful recovery.
At the first follow-up appointment, the patient’s husband told the surgeon that she had now developed a bony “spike” on her back. The surgeon was intrigued and asked the patient to reveal this spike. At examination, the spike was the inferior angle of the scapula, which appeared to be sticking out posteriorly (“winged”). Raising the arms accentuated this structure.
The medial border of the scapula was accentuated and it was noted that there was some loss of bulk of the serratus anterior muscle, which attaches to the tip of the scapula.
The nerve to this muscle was damaged.
During the surgery on the axilla, the long thoracic nerve was damaged as it passed down the lateral thoracic wall on the external surface of the serratus anterior, just deep to the skin and subcutaneous fascia.
Because the nerve was transected, it is unlikely that the patient will improve, but she was happy that she had an adequate explanation for the spike.
A 25-year-old woman was involved in a motor vehicle accident and thrown from her motorcycle. When she was admitted to the emergency room, she was unconscious. A series of tests and investigations were performed, one of which included chest radiography. The attending physician noted a complex fracture of the first rib on the left.
Many important structures that supply the upper limb pass over rib I.
It is important to test the nerves that supply the arm and hand, although this is extremely difficult to do in an unconscious patient. However, some muscle reflexes can be determined using a tendon hammer. Also, it may be possible to test for pain reflexes in patients with altered consciousness levels. Palpation of the axillary artery, brachial artery, radial artery, and ulnar artery pulses is necessary because a fracture of the first rib can sever and denude the subclavian artery, which passes over it.
A chest drain was immediately inserted because the lung had collapsed. The fractured first rib had damaged the visceral and parietal pleurae, allowing air from a torn lung to escape into the pleural cavity. The lung collapsed, and the pleural cavity filled with air, which impaired lung function. |
A tube was inserted between the ribs, and the air was sucked out to re-inflate the lung.
The first rib is a deep structure at the base of the neck. It is not uncommon for ribs to be broken after minor injuries, including sports injuries. However, rib I, which lies at the base of the neck, is surrounded by muscles and soft tissues that provide it with considerable protection. Therefore a patient with a fracture of the first rib has undoubtedly been subjected to a considerable force, which usually occurs in a deceleration injury. Other injuries should always be sought and the patient should be managed with a high level of concern for deep neck and mediastinal injuries.
A resident was asked to carry out a clinical assessment of a patient’s hand. He examined the following:
The musculoskeletal system includes the bones, joints, muscles, and tendons. The resident looked for abnormalities and muscle wasting. Knowing which areas are wasted identifies the nerve that supplies them. She palpated the individual bones and palpated the scaphoid with the wrist in ulnar deviation. She examined the movement of joints because they may be restricted by joint disease or inability of muscular contraction.
Palpation of both radial and ulnar pulses is necessary. The resident looked for capillary return to assess how well the hand was perfused.
Examination of the nerves
The three main nerves to the hand should be tested.
The median nerve innervates the skin on the palmar aspect of the lateral three and one-half digits, the dorsal aspect of the distal phalanx, half of the middle phalanges of the same fingers, and a variable amount on the radial side of the palm of the hand. Median nerve damage results in wasting of the thenar eminence, absence of abduction of the thumb, and absence of opposition of the thumb.
The ulnar nerve innervates the skin of the anterior and posterior surfaces of the little finger and the ulnar side of the ring finger, the skin over the hypothenar eminence, and a similar strip of skin posteriorly. Sometimes the ulnar nerve innervates all the skin of the ring finger and the ulnar side of the middle finger.
An ulnar nerve palsy results in wasting of the hypothenar eminence, absent flexion of the distal interphalangeal joints of the little and ring fingers, and absent abduction and adduction of the fingers. Adduction of the thumb also is affected.
The radial nerve innervates a small area of skin over the lateral aspect of metacarpal I and the back of the first web space.
The radial nerve also produces extension of the wrist and extension of the metacarpophalangeal and interphalangeal joints and of the digits.
A very simple examination would include tests for the median nerve by opposition of the thumb, for the ulnar nerve by abduction and adduction of the digits, and for the radial nerve by extension of the wrist and fingers and feeling on the back of the first web space.
A 45-year-old man came to his physician complaining of pain and weakness in his right shoulder. The pain began after a fall on his outstretched hand approximately 6 months previously. The patient recalled having some minor shoulder tenderness but no other specific symptoms. He was otherwise fit and well.
On examination of the shoulder, there was marked wasting of the muscles in the supraspinous and infraspinous fossae. The patient found initiation of abduction difficult and there was a weakness of lateral rotation of the humerus.
The wasted muscles were the supraspinatus and infraspinatus. The cause of the muscle wasting was disuse.
Muscle atrophy (wasting) occurs through a variety of disorders. Disuse atrophy is one of the most common causes. Examples of disuse atrophy include the loss of muscle bulk after fracture immobilization in a plaster cast. The opposite effect can also be demonstrated—when muscles are overused they become bulkier (hypertrophy). |
The supraspinatus and infraspinatus muscles are supplied by the suprascapular nerve (C5, C6), which originates from the superior trunk of the brachial plexus. Given that only these muscles were involved, it is highly likely that the muscle atrophy is caused by denervation. Denervation may result from a direct nerve transection, nerve compression, or a pharmacological effect on the nerve.
The typical site for compression of the suprascapular nerve is the suprascapular notch (foramen) on the superior margin of the scapula.
The patient’s apparently minor injury damaged the fibrocartilaginous glenoid labrum, which allowed a cyst to form and pass along the superior border of the scapula to the suprascapular notch (foramen), where the cyst compressed the suprascapular nerve.
Surgical excision of the damaged glenoid labrum and removal of the cyst improved the patient’s symptoms.
A surgeon wished to carry out a complex procedure on a patient’s wrist, and asked the anesthesiologist whether the whole arm could be numbed while the patient was awake. Within 20 minutes the anesthesiologist had carried out the procedure after injecting 10 mL of local anesthetic into the axilla. The surgeon went ahead with the operation and the patient did not feel a thing.
The anesthetic was injected into the axillary sheath.
It would be almost impossible to anesthetize the wrist in the forearm because local anesthetic would have to be placed accurately around the ulnar, median, and radial nerves. Furthermore, all of the cutaneous branches of the forearm would also have to be anesthetized individually, which would take a considerable amount of time and probably produce subtotal anesthesia.
The nerves of the upper limb originate from the brachial plexus, which surrounds the axillary artery within the axilla. Importantly, the axillary artery, axillary vein, and brachial plexus lie within the sleeve-like covering of fascia termed the axillary sheath. By injecting the anesthetic into the space enclosed by the axillary sheath, all of the nerves of the brachial plexus were paralyzed.
It is possible with a patient’s arm abducted and externally rotated (palm behind the head) to easily palpate the axillary artery and therefore locate the position of the axillary sheath. Once the axillary artery has been identified, a small needle can be placed beside the vessel and local anesthetic can be injected on both sides of it. The local anesthetic tracks along the axillary sheath in this region. The brachial plexus surrounding the axillary artery is therefore completely anesthetized and an effective local anesthetic “block” is achieved.
“Could there be any complications?” asks the patient.
Potential complications are a direct needle spike of the branches of the brachial plexus, damage to the axillary artery, and inadvertent arterial injection of the local anesthetic. Fortunately, these are rare in skilled hands.
A 35-year-old woman comes to her physician complaining of tingling and numbness in the fingertips of the first, second, and third digits (thumb, index, and middle fingers). The symptoms were provoked by arm extension. Local anesthesia was also present around the base of the thenar eminence.
The problem was diagnosed as median nerve compression. |
The median nerve is formed from the lateral and medial cords of the brachial plexus anterior to the axillary artery and passes into the arm anterior to the brachial artery. At the level of the elbow joint it sits medial to the brachial artery, both of which are medial to the tendon of the biceps. In the forearm the nerve courses through the anterior compartment and passes deep to the flexor retinaculum. It innervates most of the muscles of the forearm, the thenar muscles, the two lateral lumbricals, and the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and the middle of the wrist.
In this patient, the median nerve initially was believed to be trapped below the flexor retinaculum (carpal tunnel syndrome).
Carpal tunnel syndrome is a common problem in young to middle-aged patients. Typically the nerve becomes compressed within the carpal tunnel. This syndrome may be associated with a number of medical conditions, such as thyroid disease and pregnancy. Occasionally a small ganglion or a tumor situated within the carpal tunnel can also compress the nerve. Other possibilities include tenosynovitis in patients with rheumatoid arthritis.
Nerve conduction studies were performed to confirm the clinical findings. Nerve conduction studies are a series of tests that send small electrical impulses along the length of a variety of nerves in order to measure the speed at which the nerve conducts these pulses. The speed of the nerve pulse can be measured and is referred to as the latency. In our patient it was noted that the nerve had normal latency to the elbow joint; however, below the elbow joint there was increased latency.
The nerve conduction studies indicated that the compression site was at the elbow joint.
The clinical findings are not consistent with carpal tunnel syndrome. The clinician should have been alerted to this problem given that the patient experienced numbness over the thenar eminence of the hand. This clue indicates an understanding of the anatomy. Compression of the nerve within the carpal tunnel does not produce this numbness, because the small cutaneous branch that supplies this region is proximal to the flexor retinaculum.
The nerve compromise was caused by the ligament of Struthers, which is an embryological remnant of the coracobrachialis muscle. It is an extremely rare finding. Occasionally it may ossify and cross the nerve, artery, and vein to produce compression in arm extension. Although this is very rare and unusual, it illustrates the complex course of the median nerve.
After a hard day’s studying, two medical students decided to meet for coffee. The more senior student said to the freshman that he would bet him $50 that he could not lift a matchbook with a finger. The freshman placed $50 on the table and the bet was on. The senior medical student told the freshman to make a fist and place it in a palm-downward position, so that the middle phalanges of the fingers were in direct contact with the bar counter. He was then told to extend his middle finger so that it stuck forward while maintaining the middle phalanges of the index finger, the ring finger, and the little finger on the bar surface.
A matchbook was placed on top of the freshman’s middle fingernail and he was told to flip it. He couldn’t. He lost the $50.
Extension of the index, middle, ring, and little fingers is performed by the extensor digitorum muscle.
Placing the fist in a palm-down position on the table and pressing the middle phalanges onto the table effectively immobilizes the action of the extensor digitorum. The freshman was therefore unable to elevate his middle finger (which was sticking out). It is important to remember that if this same procedure is carried out leaving the index or little finger free to move, they do. This is because these two digits are extended not only by the extensor digitorum muscle but also by the extensor indicis muscle (index finger) and extensor digiti minimi muscle (little finger). |
A 70-year-old woman came to an orthopedic surgeon with right shoulder pain and failure to initiate abduction of the shoulder. Further examination revealed loss of muscle bulk in the supraspinous fossa. The supraspinatus muscle was damaged.
Abduction of the humerus at the glenohumeral joint is initiated by the supraspinatus muscle. After the shoulder has been abducted to 10°–15°, the deltoid muscle continues the movement. The patient was able to abduct her arm by lowering and tilting the glenohumeral joint inferiorly to enable the deltoid to obtain its mechanical advantage.
The loss of muscle bulk in the supraspinous fossa suggested muscle atrophy.
Muscle atrophy occurs when a muscle is not used. The orthopedic surgeon thought that there was a tear of the supraspinatus tendon beneath the acromion. If this was so, the muscle would atrophy.
The diagnosis was confirmed by ultrasound scan.
The patient was seated on a stool and her right shoulder was uncovered. The patient’s hand was placed over her right buttock, a position that acts to externally rotate and extend the shoulder, exposing the supraspinatus tendon for ultrasound scan examination. The ultrasound revealed a completely torn tendon with fluid in the subacromial subdeltoid bursa (eFig. 7.128). The patient underwent a surgical repair and made a good recovery.
A 35-year-old baseball pitcher came to the clinic with a history of a recurrent dislocation of the shoulder (eFig. 7.129). An MRI scan was performed to assess the shoulder joint prior to any treatment.
The MRI demonstrates the anatomical structures in multiple planes, allowing the physician to obtain an overview of the shoulder and to assess any intraarticular or extraarticular structures that may have been damaged and require surgical repair.
The MRI demonstrated a divot in the posterosuperior aspect of the humeral head and a small fragment of bone and glenoid labrum that had become separated in the anteroinferior aspect of the glenoid cavity.
Shoulder dislocation is not an uncommon problem and may occur as a “once-off” or with repetitive injury may be recurrent. Recurrent dislocations may be bilateral and symmetrical (a memory aid is “torn loose or born loose”).
The MRI findings are typical for an anteroinferior dislocation, which is the most common type; moreover the MRI demonstrates the injuries that occur within the joint at the time of dislocation. These injuries include the abutment of the posterosuperior aspect of the humeral head on the anteroinferior aspect of the glenoid cavity. This type of injury, when recurrent, may avulse a small fragment of the glenoid labrum, and in some cases this may attach to a small fragment of bone (the Bankart lesion). When the shoulder is relocated, the integrity of the capsular attachment anteroinferiorly has been disrupted, potentially making the shoulder somewhat prone to further dislocation.
An arthroscopic repair was performed.
Arthroscopy of the shoulder is an established method for assessing the shoulder joint. Portals of entry are anterior and posterior and small holes in the capsule are made percutaneously. The shoulder joint is filled with saline, which distends it, allowing the arthroscope to move around the joint and inspect the joint surfaces, including the labrum. The labrum and its bony fragment were reattached and sutured using anchor sutures (somewhat similar to staples). The anterior aspect of the capsule was also tightened.
The patient made an uneventful recovery.
After the procedure the arm was held in internal rotation and remained adducted. Gentle exercise and physiotherapy were performed and the patient returned to playing baseball.
821.e1 821.e2
Conceptual Overview • Relationship to Other Regions
Fig. 7.40, cont’d
Table 7.7 Branches of brachial plexus (parentheses indicate that a spinal segment is a minor component of the nerve or is inconsistently present in the nerve)—cont’d |
Fig. 7.63, cont’d
Fig. 7.66, cont’d
Regional Anatomy • Anterior Compartment of the Forearm
Regional Anatomy • Anterior Compartment of the Forearm
Regional Anatomy • Anterior Compartment of the Forearm
Regional Anatomy • Anterior Compartment of the Forearm
Regional Anatomy • Posterior Compartment of the Forearm
Regional Anatomy • Posterior Compartment of the Forearm
Regional Anatomy • Posterior Compartment of the Forearm
Regional Anatomy • Posterior Compartment of the Forearm
Fig. 7.94, cont’d
Surface Anatomy • Visualizing the Axilla and Locating Contents and Related Structures
Surface Anatomy • Identifying Tendons and Locating Major Vessels and Nerves in the Distal Forearm
Surface Anatomy • Motor Function of the Median and Ulnar Nerves in the Hand
Arrangement of meninges and spaces 865
Anterior triangle of the neck 995
Posterior triangle of the neck 1012
Root of the neck 1019
Gaps in the pharyngeal wall and structures passing through them 1035
Cavity of the larynx 1048
Function of the larynx 1053
Walls, floor, and roof 1065
Multiple nerves innervate the oral cavity 1077
Walls: the cheeks 1080
Anatomical position of the head and major landmarks 1110
Visualizing structures at the CIII/CIV and CVI vertebral levels 1111
How to outline the anterior and posterior triangles of the neck 1112
How to locate the cricothyroid ligament 1113
How to find the thyroid gland 1114
Estimating the position of the middle meningeal artery 1114
Major features of the face 1115
The eye and lacrimal apparatus 1116
The head and neck are anatomically complex areas of the body.
The head is composed of a series of compartments, which are formed by bone and soft tissues. They are: the cranial cavity, two ears, two orbits, two nasal cavities, and an oral cavity (Fig. 8.1).
The cranial cavity is the largest compartment and contains the brain and associated membranes (meninges).
Most of the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions.
The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the cranial cavity, and the apex of each cone is directed posteromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids.
The nasal cavities are the upper parts of the respiratory tract and are between the orbits. They have walls, floors, and ceilings, which are predominantly composed of bone and cartilage. The anterior openings to the nasal cavities are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures).
Continuous with the nasal cavities are air-filled extensions (paranasal sinuses), which project laterally, superiorly, and posteriorly into surrounding bones.
The largest, the maxillary sinuses, are inferior to the orbits.
The oral cavity is inferior to the nasal cavities, and separated from them by the hard and soft palates. The floor of the oral cavity is formed entirely of soft tissues.
The anterior opening to the oral cavity is the oral fissure (mouth), and the posterior opening is the oropharyngeal isthmus. Unlike the nares and choanae, which are continuously open, both the oral fissure and oropharyngeal isthmus can be opened and closed by surrounding soft tissues. |
In addition to the major compartments of the head, two other anatomically defined regions (infratemporal fossa and pterygopalatine fossa) of the head on each side are areas of transition from one compartment of the head to another (Fig. 8.2). The face and scalp also are anatomically defined areas of the head and are related to external surfaces.
The infratemporal fossa is an area between the posterior aspect (ramus) of the mandible and a flat region of bone (lateral plate of the pterygoid process) just posterior to the upper jaw (maxilla). This fossa, bounded by bone and soft tissues, is a conduit for one of the major cranial nerves—the mandibular nerve (the mandibular division of the trigeminal nerve [V3]), which passes between the cranial and oral cavities.
The pterygopalatine fossa on each side is just posterior to the upper jaw. This small fossa communicates with the cranial cavity, the infratemporal fossa, the orbit, the nasal cavity, and the oral cavity. A major structure passing through the pterygopalatine fossa is the maxillary nerve (the maxillary division of the trigeminal nerve [V2]).
The face is the anterior aspect of the head and contains a unique group of muscles that move the skin relative to underlying bone and control the anterior openings to the orbits and oral cavity (Fig. 8.3).
The scalp covers the superior, posterior, and lateral regions of the head (Fig. 8.3).
The neck extends from the head above to the shoulders and thorax below (Fig. 8.4). Its superior boundary is along the inferior margins of the mandible and bone features on the posterior aspect of the skull. The posterior neck is higher than the anterior neck to connect cervical viscera with the posterior openings of the nasal and oral cavities.
The inferior boundary of the neck extends from the top of the sternum, along the clavicle, and onto the adjacent acromion, a bony projection of the scapula. Posteriorly, the inferior limit of the neck is less well defined, but can be approximated by a line between the acromion and the spinous process of vertebra CVII, which is prominent and easily palpable. The inferior border of the neck encloses the base of the neck.
The neck has four major compartments (Fig. 8.5), which are enclosed by an outer musculofascial collar:
The vertebral compartment contains the cervical vertebrae and associated postural muscles.
The visceral compartment contains important glands (thyroid, parathyroid, and thymus), and parts of the respiratory and digestive tracts that pass between the head and thorax.
The two vascular compartments, one on each side, contain the major blood vessels and the vagus nerve.
The neck contains two specialized structures associated with the digestive and respiratory tracts—the larynx and pharynx.
The larynx (Fig. 8.6) is the upper part of the lower airway and is attached below to the top of the trachea and above, by a flexible membrane, to the hyoid bone, which in turn is attached to the floor of the oral cavity. A number of cartilages form a supportive framework for the larynx, which has a hollow central channel. The dimensions of this central channel can be adjusted by soft tissue structures associated with the laryngeal wall. The most important of these are two lateral vocal folds, which project toward each other from adjacent sides of the laryngeal cavity. The upper opening of the larynx (laryngeal inlet) is tilted posteriorly, and is continuous with the pharynx. |
The pharynx (Fig. 8.6) is a chamber in the shape of a half-cylinder with walls formed by muscles and fascia. Above, the walls are attached to the base of the skull, and below to the margins of the esophagus. On each side, the walls are attached to the lateral margins of the nasal cavities, the oral cavity, and the larynx. The two nasal cavities, the oral cavity, and the larynx therefore open into the anterior aspect of the pharynx, and the esophagus opens inferiorly.
The part of the pharynx posterior to the nasal cavities is the nasopharynx. Those parts posterior to the oral cavity and larynx are the oropharynx and laryngopharynx, respectively.
The head houses and protects the brain and all the receptor systems associated with the special senses—the nasal cavities associated with smell, the orbits with vision, the ears with hearing and balance, and the oral cavity with taste.
Contains upper parts of respiratory
The head contains the upper parts of the respiratory and digestive systems—the nasal and oral cavities—which have structural features for modifying the air or food passing into each system.
The head and neck are involved in communication. Sounds produced by the larynx are modified in the pharynx and oral cavity to produce speech. In addition, the muscles of facial expression adjust the contours of the face to relay nonverbal signals.
Positioning the head
The neck supports and positions the head. Importantly, it enables an individual to position sensory systems in the head relative to environmental cues without moving the entire body.
Connects the upper and lower respiratory and digestive tracts
The neck contains specialized structures (pharynx and larynx) that connect the upper parts of the digestive and respiratory tracts (nasal and oral cavities) in the head, with the esophagus and trachea, which begin relatively low in the neck and pass into the thorax.
The many bones of the head collectively form the skull (Fig. 8.7A). Most of these bones are interconnected by sutures, which are immovable fibrous joints (Fig. 8.7B).
In the fetus and newborn, large membranous and unossified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity (Fig. 8.7C), allow: the head to deform during its passage through the birth canal, and postnatal growth.
Most of the fontanelles close during the first year of life. Full ossification of the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life.
There are only three pairs of synovial joints on each side in the head. The largest are the temporomandibular joints between the lower jaw (mandible) and the temporal bone. The other two synovial joints are between the three tiny bones in the middle ear, the malleus, incus, and stapes.
The seven cervical vertebrae form the bony framework of the neck.
Cervical vertebrae (Fig. 8.8A) are characterized by: small bodies, bifid spinous processes, and transverse processes that contain a foramen (foramen transversarium).
Together the foramina transversaria form a longitudinal passage on each side of the cervical vertebral column for blood vessels (vertebral artery and veins) passing between the base of the neck and the cranial cavity.
The typical transverse process of a cervical vertebra also has anterior and posterior tubercles for muscle attachment. The anterior tubercles are derived from the same embryological elements that give rise to ribs in the thoracic region. Occasionally, cervical ribs develop from these elements, particularly in association with the lower cervical vertebrae.
The upper two cervical vertebrae (CI and CII) are modified for moving the head (Fig. 8.8B–E; see also
Chapter 2). |
The hyoid bone is a small U-shaped bone (Fig. 8.9A) oriented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side.
The body of the hyoid bone is anterior and forms the base of the U.
The two arms of the U (greater horns) project posteriorly from the lateral ends of the body.
The hyoid bone does not articulate directly with any other skeletal elements in the head and neck.
The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments:
Superiorly, it is attached to the floor of the oral cavity.
Inferiorly, it is attached to the larynx.
Posteriorly, it is attached to the pharynx (Fig. 8.9B).
The soft palate is a soft tissue flap-like structure “hinged” to the back of the hard palate (Fig. 8.10A) with a free posterior margin. It can be elevated and depressed by muscles (Fig. 8.10B).
The soft palate and associated structures can be clearly seen through an open mouth.
The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation.
In the head
The muscle groups in the head include: the extra-ocular muscles (move the eyeball and open the upper eyelid), muscles of the middle ear (adjust the movement of the middle ear bones), muscles of facial expression (move the face), muscles of mastication (move the jaw—temporo- mandibular joint), muscles of the soft palate (elevate and depress the palate), and muscles of the tongue (move and change the contour of the tongue).
In the neck
In the neck, major muscle groups include: muscles of the pharynx (constrict and elevate the pharynx), muscles of the larynx (adjust the dimensions of the air pathway), strap muscles (position the larynx and hyoid bone in the neck), muscles of the outer cervical collar (move the head and upper limb), and postural muscles in the muscular compartment of the neck (position the neck and head).
The superior thoracic aperture (thoracic inlet) opens directly into the base of the neck (Fig. 8.11). Structures passing between the head and thorax pass up and down through the superior thoracic aperture and the visceral compartment of the neck. At the base of the neck, the trachea is immediately anterior to the esophagus, which is directly anterior to the vertebral column. There are major veins, arteries, and nerves anterior and lateral to the trachea.
There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11):
Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax.
Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb.
In the neck, the two important vertebral levels (Fig.
8.12) are: between CIII and CIV, at approximately the superior border of the thyroid cartilage of the larynx (which can be palpated) and where the major artery on each side of the neck (the common carotid artery) bifurcates into internal and external carotid arteries; and between CV and CVI, which marks the lower limit of the pharynx and larynx, and the superior limit of the trachea and esophagus—the indentation between the cricoid cartilage of the larynx and the first tracheal ring can be palpated.
The internal carotid artery has no branches in the neck and ascends into the skull to supply much of the brain. It also supplies the eye and orbit. Other regions of the head and neck are supplied by branches of the external carotid artery.
Airway in the neck |
The larynx (Fig. 8.13) and the trachea are anterior to the digestive tract in the neck, and can be accessed directly when upper parts of the system are blocked. A cricothyrotomy makes use of the easiest route of access through the cricothyroid ligament (cricovocal membrane, cricothyroid membrane) between the cricoid and thyroid cartilages of the larynx. The ligament can be palpated in the midline, and usually there are only small blood vessels, connective tissue, and skin (though occasionally, a small lobe of the thyroid gland—pyramidal lobe) overlying it. At a lower level, the airway can be accessed surgically through the anterior wall of the trachea by tracheostomy. This route of entry is complicated because large veins and part of the thyroid gland overlie this region.
There are twelve pairs of cranial nerves and their defining feature is that they exit the cranial cavity through foramina or fissures.
All cranial nerves innervate structures in the head or neck. In addition, the vagus nerve [X] descends through the neck and into the thorax and abdomen where it innervates viscera.
Parasympathetic fibers in the head are carried out of the brain as part of four cranial nerves—the oculomotor nerve [III], the facial nerve [VII], the glossopharyngeal nerve [IX], and the vagus nerve [X] (Fig. 8.14). Parasympathetic fibers in the oculomotor nerve [III], the facial nerve [VII], and the glossopharyngeal nerve [IX] destined for target tissues in the head leave these nerves, and are distributed with branches of the trigeminal nerve [V].
The vagus nerve [X] leaves the head and neck to deliver parasympathetic fibers to the thoracic and abdominal viscera.
There are eight cervical nerves (C1 to C8):
C1 to C7 emerge from the vertebral canal above their respective vertebrae.
C8 emerges between vertebrae CVII and TI (Fig. 8.15A).
The anterior rami of C1 to C4 form the cervical plexus. The major branches from this plexus supply the strap muscles, the diaphragm (phrenic nerve), skin on the anterior and lateral parts of the neck, skin on the upper anterior thoracic wall, and skin on the inferior parts of the head (Fig. 8.15B).
The anterior rami of C5 to C8, together with a large component of the anterior ramus of T1, form the brachial plexus, which innervates the upper limb.
Functional separation of the digestive
The pharynx is a common chamber for the digestive and respiratory tracts. Consequently, breathing can take place through the mouth as well as through the nose, and material from the oral cavity can potentially enter either the esophagus or the larynx. Importantly:
The lower airway can be accessed through the oral cavity by intubation.
The digestive tract (esophagus) can be accessed through the nasal cavity by feeding tubes.
Normally, the soft palate, epiglottis, and soft tissue structures within the larynx act as valves to prevent food and liquid from entering lower parts of the respiratory tract (Fig. 8.16A).
During normal breathing, the airway is open and air passes freely through the nasal cavities (or oral cavity), pharynx, larynx, and trachea (Fig. 8.16A). The lumen of the esophagus is normally closed because, unlike the airway, it has no skeletal support structures to hold it open.
When the oral cavity is full of liquid or food, the soft palate is swung down (depressed) to close the oropharyngeal isthmus, thereby allowing manipulation of food and fluid in the oral cavity while breathing (Fig. 8.16C). |
When swallowing, the soft palate and parts of the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D).
The soft palate elevates to open the oropharyngeal isthmus while at the same time sealing off the nasal part of the pharynx from the oral part. This prevents food and fluid from moving upward into the nasopharynx and nasal cavities.
The epiglottis of the larynx closes the laryngeal inlet and much of the laryngeal cavity becomes occluded by opposition of the vocal folds and soft tissue folds superior to them. In addition, the larynx is pulled up and forward to facilitate the moving of food and fluid over and around the closed larynx and into the esophagus.
In newborns, the larynx is high in the neck and the epiglottis is above the level of the soft palate (Fig. 8.16E). Babies can therefore suckle and breathe at the same time. Liquid flows around the larynx without any danger of entering the airway. During the second year of life, the larynx descends into the low cervical position characteristic of adults.
Triangles of the neck
The two muscles (trapezius and sternocleidomastoid) that form part of the outer cervical collar divide the neck into anterior and posterior triangles on each side (Fig. 8.17).
The boundaries of each anterior triangle are: the median vertical line of the neck, the inferior margin of the mandible, and the anterior margin of the sternocleidomastoid muscle.
The posterior triangle is bounded by: the middle one-third of the clavicle, the anterior margin of the trapezius, and the posterior margin of the sternocleidomastoid.
Major structures that pass between the head and thorax can be accessed through the anterior triangle.
The posterior triangle in part lies over the axillary inlet, and is associated with structures (nerves and vessels) that pass into and out of the upper limb.
The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form the cranium.
The cranium can be subdivided into: an upper domed part (the calvaria), which covers the cranial cavity containing the brain, a base that consists of the floor of the cranial cavity, and a lower anterior part—the facial skeleton (viscerocranium).
The bones forming the calvaria are mainly the paired temporal and parietal bones, and parts of the unpaired frontal, sphenoid, and occipital bones.
The bones forming the base of the cranium are mainly parts of the sphenoid, temporal, and occipital bones.
The bones forming the facial skeleton are the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae and inferior nasal conchae and the unpaired vomer.
The mandible is not part of the cranium nor part of the facial skeleton.
The anterior view of the skull includes the forehead superiorly, and, inferiorly, the orbits, the nasal region, the part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw (Fig. 8.18).
The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18).
Just superior to the rim of the orbit on each side are the raised superciliary arches. These are more pronounced in men than in women. Between these arches is a small depression (the glabella).
Clearly visible in the medial part of the superior rim of each orbit is the supra-orbital foramen (supra-orbital notch; Table 8.1).
Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit. |
Laterally, the zygomatic process of the frontal bone projects inferiorly forming the upper lateral rim of the orbit. This process articulates with the frontal process of the zygomatic bone.
The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit is formed by the zygomatic bone (the cheekbone).
Superiorly, in the nasal region the paired nasal bones articulate with each other in the midline, and with the frontal bone superiorly. The center of the frontonasal suture formed by the articulation of the nasal bones and the frontal bone is the nasion.
Laterally, each nasal bone articulates with the frontal process of each maxilla.
Inferiorly, the piriform aperture is the large opening in the nasal region and the anterior opening of the nasal cavity. It is bounded superiorly by the nasal bones and laterally and inferiorly by each maxilla.
Visible through the piriform aperture are the fused nasal crests, forming the lower part of the bony nasal septum and ending anteriorly as the anterior nasal spine, and the paired inferior nasal conchae.
The part of the face between the orbit and the upper teeth and each upper jaw is formed by the paired maxillae.
Superiorly, each maxilla contributes to the inferior and medial rims of the orbit.
Laterally, the zygomatic process of each maxilla articulates with the zygomatic bone and medially, the frontal process of each maxilla articulates with the frontal bone.
Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of the maxilla.
On the anterior surface of the body of the maxilla, just below the inferior rim of the orbit, is the infra-orbital foramen (Table 8.1).
Inferiorly, each maxilla ends as the alveolar process, which contains the teeth and forms the upper jaw.
The lower jaw (mandible) is the most inferior structure in the anterior view of the skull. It consists of the body of the mandible anteriorly and the ramus of the mandible posteriorly. These meet posteriorly at the angle of the mandible. All these parts of the mandible are visible, to some extent, in the anterior view.
The body of the mandible is arbitrarily divided into two parts:
The lower part is the base of the mandible.
The upper part is the alveolar part of the mandible.
The alveolar part of the mandible contains the teeth and is resorbed when the teeth are removed. The base of the mandible has a midline swelling (the mental protuberance) on its anterior surface where the two sides of the mandible come together. Just lateral to the mental protuberance, on either side, are slightly more pronounced bumps (mental tubercles).
Laterally, a mental foramen (Table 8.1) is visible halfway between the upper border of the alveolar part of the mandible and the lower border of the base of the mandible. Continuing past this foramen is a ridge (the oblique line) passing from the front of the ramus onto the body of the mandible. The oblique line is a point of attachment for muscles that depress the lower lip.
The lateral view of the skull consists of the lateral wall of the cranium, which includes lateral portions of the calvaria and the facial skeleton, and half of the lower jaw (Fig. 8.19):
Bones forming the lateral portion of the calvaria include the frontal, parietal, occipital, sphenoid, and temporal bones.
Bones forming the visible part of the facial skeleton include the nasal, maxilla, and zygomatic bones.
The mandible forms the visible part of the lower jaw.
Lateral portion of the calvaria
The lateral portion of the calvaria begins anteriorly with the frontal bone. In upper regions, the frontal bone articulates with the parietal bone at the coronal suture. The parietal bone then articulates with the occipital bone at the lambdoid suture. |
In lower parts of the lateral portion of the calvaria, the frontal bone articulates with the greater wing of the sphenoid bone (Fig. 8.19), which then articulates with the parietal bone at the sphenoparietal suture, and with the anterior edge of the temporal bone at the sphenosquamous suture.
The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is the pterion. The clinical consequences of a skull fracture in this area can be very serious. The bone in this area is particularly thin and overlies the anterior division of the middle meningeal artery, which can be torn by a skull fracture in this area, resulting in an extradural hematoma.
The final articulation across the lower part of the lateral portion of the calvaria is between the temporal bone and the occipital bone at the occipitomastoid suture.
A major contributor to the lower portion of the lateral wall of the cranium is the temporal bone (Fig. 8.19), which consists of several parts:
The squamous part has the appearance of a large flat plate, forms the anterior and superior parts of the temporal bone, contributes to the lateral wall of the cranium, and articulates anteriorly with the greater wing of the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly at the squamous suture.
The zygomatic process is an anterior bony projection from the lower surface of the squamous part of the temporal bone that initially projects laterally and then curves anteriorly to articulate with the temporal process of the zygomatic bone to form the zygomatic arch.
Immediately below the origin of the zygomatic process from the squamous part of the temporal bone is the tympanic part of the temporal bone, and clearly visible on the surface of this part is the external acoustic opening leading to the external acoustic meatus (ear canal).
The petromastoid part, which is usually separated into a petrous part and a mastoid part for descriptive purposes.
The mastoid part is the most posterior part of the temporal bone, and is the only part of the petromastoid part of the temporal bone seen on a lateral view of the skull. It is continuous with the squamous part of the temporal bone anteriorly, and articulates with the parietal bone superiorly at the parietomastoid suture, and with the occipital bone posteriorly at the occipitomastoid suture. These two sutures are continuous with each other, and the parietomastoid suture is continuous with the squamous suture.
Inferiorly, a large bony prominence (the mastoid process) projects from the inferior border of the mastoid part of the temporal bone. This is a point of attachment for several muscles.
Medial to the mastoid process, the styloid process projects from the lower border of the temporal bone.
Visible part of the facial skeleton
The bones of the viscerocranium visible in a lateral view of the skull include the nasal, maxilla, and zygomatic bones (Fig. 8.19) as follows:
A nasal bone anteriorly.
The maxilla with its alveolar process containing teeth forming the upper jaw; anteriorly, it articulates with the nasal bone; superiorly, it contributes to the formation of the inferior and medial borders of the orbit; medially, its frontal process articulates with the frontal bone; laterally, its zygomatic process articulates with the zygomatic bone. |
The zygomatic bone, an irregularly shaped bone with a rounded lateral surface that forms the prominence of the cheek, is a visual centerpiece in this view— medially, it assists in the formation of the inferior rim of the orbit through its articulation with the zygomatic process of the maxilla; superiorly, its frontal process articulates with the zygomatic process of the frontal bone assisting in the formation of the lateral rim of the orbit; laterally, seen prominently in this view of the skull, the horizontal temporal process of the zygomatic bone projects backward to articulate with the zygomatic process of the temporal bone and so form the zygomatic arch.
Usually a small foramen (the zygomaticofacial foramen; Table 8.1) is visible on the lateral surface of the zygomatic bone. A zygomaticotemporal foramen is present on the medial deep surface of the bone.
The final bony structure visible in a lateral view of the skull is the mandible. Inferiorly in the anterior part of this view, it consists of the anterior body of the mandible, a posterior ramus of the mandible, and the angle of the mandible where the inferior margin of the mandible meets the posterior margin of the ramus (Fig. 8.19).
The teeth are in the alveolar part of the body of the mandible and the mental protuberance is visible in this view.
The mental foramen is on the lateral surface of the body, and on the superior part of the ramus condylar and coronoid processes extend upward.
The condylar process is involved in articulation of the mandible with the temporal bone, and the coronoid process is the point of attachment for the temporalis muscle.
The occipital, parietal, and temporal bones are seen in the posterior view of the skull.
Centrally the flat or squamous part of the occipital bone is the main structure in this view of the skull (Fig. 8.20). It articulates superiorly with the paired parietal bones at the lambdoid suture and laterally with each temporal bone at the occipitomastoid sutures. Along the lambdoid suture small islands of bone (sutural bones or wormian bones) may be observed.
Several bony landmarks are visible on the occipital bone. There is a midline projection (the external occipital protuberance) with curved lines extending laterally from it (superior nuchal lines). The most prominent point of the external occipital protuberance is the inion. About 1 inch (2.5 cm) below the superior nuchal lines two additional lines (the inferior nuchal lines) curve laterally. Extending downward from the external occipital protuberance is the external occipital crest.
Laterally, the temporal bones are visible in the posterior view of the skull, with the mastoid processes being the prominent feature (Fig. 8.20). On the inferomedial border of each mastoid process is a notch (the mastoid notch), which is a point of attachment for the posterior belly of the digastric muscle.
The frontal bone, parietal bones, and occipital bone are seen in a superior view of the skull (Fig. 8.21). These bones make up the superior part of the calvaria or the calva (skullcap).
In an anterior to posterior direction:
The unpaired frontal bone articulates with the paired parietal bones at the coronal suture.
The two parietal bones articulate with each other in the midline at the sagittal suture.
The parietal bones articulate with the unpaired occipital bone at the lambdoid suture.
The junction of the sagittal and coronal sutures is the bregma, and the junction of the sagittal and lambdoid sutures is the lambda.
The only foramina visible in this view of the skull may be the paired parietal foramina, posteriorly, one on each parietal bone just lateral to the sagittal suture (Fig. 8.21). |
The bones making up the calvaria (Fig. 8.22) are unique in their structure, consisting of dense internal and external tables of compact bone separated by a layer of spongy bone (the diploë).
The base of the skull is seen in the inferior view and extends anteriorly from the middle incisor teeth posteriorly to the superior nuchal lines and laterally to the mastoid processes and zygomatic arches (Fig. 8.23).
For descriptive purposes the base of the skull is often divided into: an anterior part, which includes the teeth and the hard palate, a middle part, which extends from behind the hard palate to the anterior margin of the foramen magnum, and a posterior part, which extends from the anterior edge of the foramen magnum to the superior nuchal lines.
The main features of the anterior part of the base of the skull are the teeth and the hard palate.
The teeth project from the alveolar processes of the two maxillae. These processes are together arranged in a U-shaped alveolar arch that borders the hard palate on three sides (Fig. 8.23).
The hard palate is composed of the palatine processes of each maxilla anteriorly and the horizontal plates of each palatine bone posteriorly.
The paired palatine processes of each maxilla meet in the midline at the intermaxillary suture, the paired maxillae and the paired palatine bones meet at the palatomaxillary suture, and the paired horizontal plates of each palatine bone meet in the midline at the interpalatine suture.
Several additional features are also visible when the hard palate is examined: the incisive fossa in the anterior midline immediately posterior to the teeth, the walls of which contain incisive foramina (the openings of the incisive canals, which are passageways between the hard palate and nasal cavity); the greater palatine foramina near the posterolateral border of the hard palate on each side, which lead to greater palatine canals; just posterior to the greater palatine foramina, the lesser palatine foramina in the pyramidal process of each palatine bone, which lead to lesser palatine canals; a midline pointed projection (the posterior nasal spine) in the free posterior border of the hard palate.
The middle part of the base of the skull is complex:
Forming the anterior half are the vomer and sphenoid bones.
Forming the posterior half are the occipital and paired temporal bones.
Anteriorly, the small vomer is in the midline, resting on the sphenoid bone (Fig. 8.23). It contributes to the formation of the bony nasal septum separating the two choanae.
Most of the anterior part of the middle part of the base of the skull consists of the sphenoid bone.
The sphenoid bone is made up of a centrally placed body, paired greater and lesser wings projecting laterally from the body, and two downward projecting pterygoid processes immediately lateral to each choana.
Three parts of the sphenoid bone, the body, greater wings, and pterygoid processes, are seen in the inferior view of the skull (Fig. 8.23). The lesser wing of the sphenoid is not seen in the inferior view.
The body of the sphenoid is a centrally placed cube of bone containing two large air sinuses separated by a septum.
It articulates anteriorly with the vomer, ethmoid, and palatine bones, posterolaterally with the temporal bones, and posteriorly with the occipital bone.
Extending downward from the junction of the body and the greater wings are the pterygoid processes (Fig. 8.23). Each of these processes consists of a narrow medial plate and broader lateral plate separated by the pterygoid fossa.
Each medial plate of the pterygoid process ends inferiorly with a hook-like projection, the pterygoid hamulus, and divides superiorly to form the small, shallow scaphoid fossa. |
Just superior to the scaphoid fossa, at the root of the medial plate of the pterygoid process is the opening of the pterygoid canal, which passes forward from near the anterior margin of the foramen lacerum.
Lateral to the lateral plate of the pterygoid process is the greater wing of the sphenoid (Fig. 8.23), which not only forms a part of the base of the skull but also continues laterally to form part of the lateral wall of the skull. It articulates laterally and posteriorly with parts of the temporal bone.
Important features visible on the surface of the greater wing in an inferior view of the skull are the foramen ovale and the foramen spinosum on the posterolateral border extending outward from the upper end of the lateral plate of the pterygoid process.
In the posterior half of the middle part of the base of the skull are the occipital bone and the paired temporal bones (Fig. 8.23).
The occipital bone, or more specifically its basilar part, is in the midline immediately posterior to the body of the sphenoid. It extends posteriorly to the foramen magnum and is bounded laterally by the temporal bones.
Prominent on the basilar part of the occipital bone is the pharyngeal tubercle, a bony protuberance for the attachment of parts of the pharynx to the base of the skull (Fig. 8.23).
Immediately lateral to the basilar part of the occipital bone is the petrous part of the petromastoid part of each temporal bone.
Wedge-shaped in its appearance, with its apex anteromedial, the petrous part of the temporal bone is between the greater wing of the sphenoid anteriorly and the basilar part of the occipital bone posteriorly. The apex forms one of the boundaries of the foramen lacerum, an irregular opening filled in life with cartilage (Fig. 8.23).
The other boundaries of the foramen lacerum are the basilar part of the occipital bone medially and the body of the sphenoid anteriorly.
Posterolateral from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the carotid canal.
Between the petrous part of the temporal bone and the greater wing of the sphenoid is a groove for the cartilaginous part of the pharyngotympanic tube (auditory tube). This groove continues posterolaterally into a bony canal in the petrous part of the temporal bone for the pharyngotympanic tube.
Just lateral to the greater wing of the sphenoid is the squamous part of the temporal bone, which participates in the temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the mandible articulates with the base of the skull. An important feature of this articulation is the prominent articular tubercle, which is the downward projection of the anterior border of the mandibular fossa (Fig. 8.23).
The posterior part of the base of the skull extends from the anterior edge of the foramen magnum posteriorly to the superior nuchal lines (Fig. 8.23). It consists of parts of the occipital bone centrally and the temporal bones laterally.
The occipital bone is the major bony element of this part of the base of the skull (Fig. 8.23). It has four parts organized around the foramen magnum, which is a prominent feature of this part of the base of the skull and through which the brain and spinal cord are continuous.
The parts of the occipital bone are the squamous part, which is posterior to the foramen magnum, the lateral parts, which are lateral to the foramen magnum, and the basilar part, which is anterior to the foramen magnum (Fig. 8.23).
The squamous and lateral parts are components of the posterior part of the base of the skull. |
The most visible feature of the squamous part of the occipital bone when examining the inferior view of the skull is a ridge of bone (the external occipital crest), which extends downward from the external occipital protuberance toward the foramen magnum. The inferior nuchal lines arc laterally from the midpoint of the crest.
Immediately lateral to the foramen magnum are the lateral parts of the occipital bones, which contain numerous important structural features.
On each anterolateral border of the foramen magnum are the rounded occipital condyles (Fig. 8.23). These paired structures articulate with the atlas (vertebra CI). Posterior to each condyle is a depression (the condylar fossa) containing a condylar canal, and anterior and superior to each condyle is the large hypoglossal canal. Lateral to each hypoglossal canal is a large, irregular jugular foramen formed by opposition of the jugular notch of the occipital bone and jugular notch of the temporal bone.
Laterally in the posterior part of the base of the skull is the temporal bone. The parts of the temporal bone seen in this location are the mastoid part of the petromastoid part and the styloid process (Fig. 8.23).
The lateral edge of the mastoid part is identified by the large cone-shaped mastoid process projecting from its inferior surface. This prominent bony structure is the point of attachment for several muscles. On the medial aspect of the mastoid process is the deep mastoid notch, which is also an attachment point for a muscle.
Anteromedial to the mastoid process is the needle-shaped styloid process projecting from the lower border of the temporal bone. The styloid process is also a point of attachment for numerous muscles and ligaments.
Finally, between the styloid process and the mastoid process is the stylomastoid foramen.
The cranial cavity is the space within the cranium that contains the brain, meninges, proximal parts of the cranial nerves, blood vessels, and cranial venous sinuses.
The calvaria is the dome-shaped roof that protects the superior aspect of the brain. It consists mainly of the frontal bone anteriorly, the paired parietal bones in the middle, and the occipital bone posteriorly (Fig. 8.24).
Sutures visible internally include: the coronal suture, between the frontal and parietal bones, the sagittal suture, between the paired parietal bones, and the lambdoid suture, between the parietal and occipital bones.
Visible junctions of these sutures are the bregma, where the coronal and sagittal sutures meet, and the lambda, where the lambdoid and sagittal sutures meet.
Other markings on the internal surface of the calva include bony ridges and numerous grooves and pits.
From anterior to posterior, features seen on the bony roof of the cranial cavity are: a midline ridge of bone extending from the surface of the frontal bone (the frontal crest), which is a point of attachment for the falx cerebri (a specialization of the dura mater that partially separates the two cerebral hemispheres); at the superior point of the termination of the frontal crest the beginning of the groove for the superior sagittal sinus, which widens and deepens posteriorly and marks the position of the superior sagittal sinus (an intradural venous structure); on either side of the groove for the superior sagittal sinus throughout its course, a small number of depressions and pits (the granular foveolae), which mark the location of arachnoid granulations (prominent structures readily identifiable when a brain with its meningeal coverings is examined; the arachnoid granulations are involved in the reabsorption of cerebrospinal fluid); and on the lateral aspects of the roof of the cranial cavity, smaller grooves created by various meningeal vessels.
The floor of the cranial cavity is divided into anterior, middle, and posterior cranial fossae. |
Parts of the frontal, ethmoid, and sphenoid bones form the anterior cranial fossa (Fig. 8.25). Its floor is composed of: frontal bone in the anterior and lateral direction, ethmoid bone in the midline, and two parts of the sphenoid bone posteriorly, the body (midline) and the lesser wings (laterally).
The anterior cranial fossa is above the nasal cavity and the orbits, and it is filled by the frontal lobes of the cerebral hemispheres.
Anteriorly, a small wedge-shaped midline crest of bone (the frontal crest) projects from the frontal bone. This is a point of attachment for the falx cerebri. Immediately posterior to the frontal crest is the foramen cecum (Table 8.2). This foramen between the frontal and ethmoid bones may transmit emissary veins connecting the nasal cavity with the superior sagittal sinus.
Posterior to the frontal crest is a prominent wedge of bone projecting superiorly from the ethmoid (the crista galli). This is another point of attachment for the falx cerebri, which is the vertical extension of dura mater partially separating the two cerebral hemispheres.
Lateral to the crista galli is the cribriform plate of the ethmoid bone (Fig. 8.25). This is a sieve-like structure, which allows small olfactory nerve fibers to pass through its foramina from the nasal mucosa to the olfactory bulb. The olfactory nerves are commonly referred to collectively as the olfactory nerve [I].
On each side of the ethmoid, the floor of the anterior cranial fossa is formed by relatively thin plates of frontal bone (the orbital part of the frontal bone), which also forms the roof of the orbit below. Posterior to both the frontal and ethmoid bones, the rest of the floor of the anterior cranial fossa is formed by the body and lesser wings of the sphenoid. In the midline, the body extends anteriorly between the orbital parts of the frontal bone to reach the ethmoid bone and posteriorly it extends into the middle cranial fossa.
The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechiasmatic sulcus, a smooth groove stretching between the optic canals across the body of the sphenoid.
Lesser wings of the sphenoid
The two lesser wings of the sphenoid project laterally from the body of the sphenoid and form a distinct boundary between the lateral parts of the anterior and middle cranial fossae.
Overhanging the anterior part of the middle cranial fossae, each lesser wing ends laterally as a sharp point at the junction of the frontal bone and the greater wing of the sphenoid near the upper lateral edge of the superior orbital fissure that is formed between the greater and lesser wings.
Medially each lesser wing widens, curves posteriorly, and ends as a rounded anterior clinoid process (Fig. 8.25). These processes serve as the anterior point of attachment for the tentorium cerebelli, which is a sheet of dura that separates the posterior part of the cerebral hemispheres from the cerebellum. Just anterior to each anterior clinoid process is a circular opening in the lesser wing of the sphenoid (the optic canal), through which the ophthalmic artery and optic nerve [II] pass as they exit the cranial cavity to enter the orbit. The optic canals are usually included in the middle cranial fossa.
The middle cranial fossa consists of parts of the sphenoid and temporal bones (Fig. 8.26).
The boundary between the anterior and middle cranial fossae in the midline is the anterior edge of the prechiasmatic sulcus, which is a smooth groove stretching between the optic canals across the body of the sphenoid.
The posterior boundaries of the middle cranial fossa are formed by the anterior surface, as high as the superior border, of the petrous part of the petromastoid part of the temporal bone. |
The floor in the midline of the middle cranial fossa is elevated and formed by the body of the sphenoid. Lateral to this are large depressions formed on either side by the greater wing of the sphenoid and the squamous part of the temporal bone. These depressions contain the temporal lobes of the brain.
Just posterior to the chiasmatic sulcus is the uniquely modified remainder of the body of the sphenoid (the sella turcica), which consists of a deep central area (the hypophyseal fossa) containing the pituitary gland with anterior and posterior vertical walls of bone (Fig. 8.26).
The anterior wall of the sella is vertical in position with its superior extent visible as a slight elevation (the tuberculum sellae) at the posterior edge of the chiasmatic sulcus.
Lateral projections from the corners of the tuberculum sellae (the middle clinoid processes) are sometimes evident.
The posterior wall of the sella turcica is the dorsum sellae, a large ridge of bone projecting upward and forward. At the top of this bony ridge the lateral edges contain rounded projections (the posterior clinoid processes), which are points of attachment, like the anterior clinoid processes, for the tentorium cerebelli.
Lateral to each side of the body of the sphenoid, the floor of the middle cranial fossa is formed on either side by the greater wing of the sphenoid (Fig. 8.26).
A diagonal gap, the superior orbital fissure, separates the greater wing of the sphenoid from the lesser wing and is a major passageway between the middle cranial fossa and the orbit. Passing through the fissure are the oculomotor nerve [III], the trochlear nerve [IV], the ophthalmic nerve [V1], the abducent nerve [VI], and ophthalmic veins.
Posterior to the medial end of the superior orbital fissure on the floor of the middle cranial fossa is a rounded foramen projecting in an anterior direction (the foramen rotundum), through which the maxillary nerve [V2] passes from the middle cranial fossa to the pterygopalatine fossa.
Posterolateral to the foramen rotundum is a large oval opening (the foramen ovale), which allows structures to pass between the extracranial infratemporal fossa and the middle cranial fossa. The mandibular nerve [V3], lesser petrosal nerve (carrying fibers from the tympanic plexus that originally came from the glossopharyngeal nerve [IX]) and, occasionally, a small vessel (the accessory middle meningeal artery), pass through this foramen.
Posterolateral from the foramen ovale is the small foramen spinosum (Fig. 8.26). This opening also connects the infratemporal fossa with the middle cranial fossa. The middle meningeal artery and its associated veins pass through this foramen and, once inside, the groove for the middle meningeal artery across the floor and lateral wall of the middle cranial fossa clearly marks their path.
Posteromedial to the foramen ovale is the rounded intracranial opening of the carotid canal. Directly inferior to this opening is an irregular foramen (the foramen lacerum) (Fig. 8.26). Clearly observed in the inferior view of the skull, the foramen lacerum is closed in life by a cartilaginous plug, and no structures pass through it completely.
The posterior boundary of the middle cranial fossa is formed by the anterior surface of the petrous part of the petromastoid part of the temporal bone.
Medially, there is a slight depression (trigeminal impression) in the anterior surface of the petrous part of the temporal bone (Fig. 8.26), which marks the location of the sensory ganglion for the trigeminal nerve [V]. |
Lateral to the trigeminal impression and on the anterior surface of the petrous part of the temporal bone is a small linear groove that passes in a superolateral direction and ends in a foramen (the groove and hiatus for the greater petrosal nerve). The greater petrosal nerve is a branch of the facial nerve [VII].
Anterolateral to the groove for the greater petrosal nerve is a second, smaller groove and hiatus for the lesser petrosal nerve, a branch from the tympanic plexus carrying fibers that originally came from the glossopharyngeal nerve [IX] (Fig. 8.26).
Above and lateral to the small openings for the greater and lesser petrosal nerves, near the superior ridge of the petrous part of the temporal bone, is a rounded protrusion of bone (the arcuate eminence) produced by the underlying anterior semicircular canal of the inner ear.
Just anterior and lateral to the arcuate eminence the anterior surface of the petrous part of the temporal bone is slightly depressed. This region is the tegmen tympani, and marks the thin bony roof of the middle ear cavity.
The posterior cranial fossa consists mostly of parts of the temporal and occipital bones, with small contributions from the sphenoid and parietal bones (Fig. 8.27). It is the largest and deepest of the three cranial fossae and contains the brainstem (midbrain, pons, and medulla) and the cerebellum.
The anterior boundaries of the posterior cranial fossa in the midline are the dorsum sellae and the clivus (Fig. 8.27). The clivus is a slope of bone that extends upward from the foramen magnum. It is formed by contributions from the body of the sphenoid and from the basilar part of the occipital bone.
Laterally the anterior boundaries of the posterior cranial fossa are the superior border of the petrous part of the petromastoid part of the temporal bone.
Posteriorly the squamous part of the occipital bone to the level of the transverse groove is the major boundary, while laterally the petromastoid part of the temporal bone and small parts of the occipital and parietal bones border the fossa.
Centrally, in the deepest part of the posterior cranial fossa, is the largest foramen in the skull, the foramen magnum. It is surrounded by the basilar part of the occipital bone anteriorly, the lateral parts of the occipital bone on either side, and the squamous part of the occipital bone posteriorly.
The spinal cord passes superiorly through the foramen magnum to continue as the brainstem.
Also passing through the foramen magnum are the vertebral arteries, the meninges, and the spinal roots of the accessory nerve [XI].
The clivus slopes upward from the foramen magnum. Lateral to the clivus is a groove for the inferior petrosal sinus between the basilar part of the occipital bone and the petrous part of the petromastoid part of the temporal bone (Fig. 8.27).
Laterally, across the upper half of the posterior surface of the petrous part of the temporal bone, is an oval foramen (the internal acoustic meatus). The facial [VII] and vestibulocochlear [VIII] nerves, and the labyrinthine artery pass through it.
Inferior to the internal acoustic meatus the temporal bone is separated from the occipital bone by the large jugular foramen (Fig. 8.27). Leading to this foramen from the medial side is the groove for the inferior petrosal sinus, and from the lateral side the groove for the sigmoid sinus.
The sigmoid sinus passes into the jugular foramen, and is continuous with the internal jugular vein, while the inferior petrosal sinus empties into the internal jugular vein in the area of the jugular foramen. |
Also passing through the jugular foramen are the glossopharyngeal nerve [IX], the vagus nerve [X], and the accessory nerve [XI].
Medial to the jugular foramen is a large rounded mound of the occipital bone (the jugular tubercle). Just inferior to this, and superior to the foramen magnum, is the hypoglossal canal, through which the hypoglossal nerve [XII] leaves the posterior cranial fossa, and a meningeal branch of the ascending pharyngeal artery enters the posterior cranial fossa.
Just posterolateral to the hypoglossal canal is the small condylar canal that, when present, transmits an emissary vein.
Squamous part of the occipital bone
The squamous part of the occipital bone has several prominent features (Fig. 8.27):
Running upward in the midline from the foramen magnum is the internal occipital crest.
On either side of the internal occipital crest, the floor of the posterior cranial fossa is concave to accommodate the cerebellar hemispheres.
The internal occipital crest ends superiorly in a bony prominence (the internal occipital protuberance).
Extending laterally from the internal occipital protuberance are grooves produced by the transverse sinuses, which continue laterally, eventually joining a groove for each sigmoid sinus—each of these grooves then turns inferiorly toward the jugular foramina.
The transverse and sigmoid sinuses are intradural venous sinuses.
Foramina and fissures through which major structures enter and leave the cranial cavity
Foramina and fissures through which major structures pass between the cranial cavity and other regions are summarized in Fig. 8.28.
The brain, as well as the spinal cord, is surrounded by three layers of membranes (the meninges, Fig. 8.31A)—a tough, outer layer (the dura mater), a delicate, middle layer (the arachnoid mater), and an inner layer firmly attached to the surface of the brain (the pia mater).
The cranial meninges are continuous with, and similar to, the spinal meninges through the foramen magnum, with one important distinction—the cranial dura mater consists of two layers, and only one of these is continuous through the foramen magnum (Fig. 8.31B).
The cranial dura mater is a thick, tough, outer covering of the brain. It consists of an outer periosteal layer and an inner meningeal layer (Fig. 8.31A):
The outer periosteal layer is firmly attached to the skull, is the periosteum of the cranial cavity, contains the meningeal arteries, and is continuous with the periosteum on the outer surface of the skull at the foramen magnum and other intracranial foramina (Fig. 8.31B).
The inner meningeal layer is in close contact with the arachnoid mater and is continuous with the spinal dura mater through the foramen magnum.
The two layers of dura separate from each other at numerous locations to form two unique types of structures (Fig. 8.31A): dural partitions, which project inward and incompletely separate parts of the brain, and intracranial venous structures.
The dural partitions project into the cranial cavity and partially subdivide the cranial cavity. They include the falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae.
The falx cerebri (Fig. 8.32) is a crescent-shaped downward projection of meningeal dura mater from the dura lining the calva that passes between the two cerebral hemispheres. It is attached anteriorly to the crista galli of the ethmoid bone and frontal crest of the frontal bone. Posteriorly it is attached to and blends with the tentorium cerebelli. |
The tentorium cerebelli (Fig. 8.32) is a horizontal projection of the meningeal dura mater that covers and separates the cerebellum in the posterior cranial fossa from the posterior parts of the cerebral hemispheres. It is attached posteriorly to the occipital bone along the grooves for the transverse sinuses. Laterally, it is attached to the superior border of the petrous part of the temporal bone, ending anteriorly at the anterior and posterior clinoid processes.
The anterior and medial borders of the tentorium cerebelli are free, forming an oval opening in the midline (the tentorial notch), through which the midbrain passes.
The falx cerebelli (Fig. 8.32) is a small midline projection of meningeal dura mater in the posterior cranial fossa. It is attached posteriorly to the internal occipital crest of the occipital bone and superiorly to the tentorium cerebelli. Its anterior edge is free and is between the two cerebellar hemispheres.
The final dural projection is the diaphragma sellae (Fig. 8.32). This small horizontal shelf of meningeal dura mater covers the hypophyseal fossa in the sella turcica of the sphenoid bone. There is an opening in the center of the diaphragma sellae through which passes the infundibulum, connecting the pituitary gland with the base of the brain, and any accompanying blood vessels.
The arterial supply to the dura mater (Fig. 8.33) travels in the outer periosteal layer of the dura and consists of: anterior meningeal arteries in the anterior cranial fossa, the middle and accessory meningeal arteries in the middle cranial fossa, and the posterior meningeal artery and other meningeal branches in the posterior cranial fossa.
All are small arteries except for the middle meningeal artery, which is much larger and supplies the greatest part of the dura.
The anterior meningeal arteries are branches of the ethmoidal arteries.
The middle meningeal artery is a branch of the maxillary artery. It enters the middle cranial fossa through the foramen spinosum and divides into anterior and posterior branches:
The anterior branch passes in an almost vertical direction to reach the vertex of the skull, crossing the pterion during its course.
The posterior branch passes in a posterosuperior direction, supplying this region of the middle cranial fossa.
The accessory meningeal artery is usually a small branch of the maxillary artery that enters the middle cranial fossa through the foramen ovale and supplies areas medial to this foramen.
The posterior meningeal artery and other meningeal branches supplying the dura mater in the posterior cranial fossa come from several sources (Fig. 8.33):
The posterior meningeal artery, the terminal branch of the ascending pharyngeal artery, enters the posterior cranial fossa through the jugular foramen.
A meningeal branch from the ascending pharyngeal artery enters the posterior cranial fossa through the hypoglossal canal.
Meningeal branches from the occipital artery enter the posterior cranial fossa through the jugular foramen and the mastoid foramen.
A meningeal branch from the vertebral artery arises as the vertebral artery enters the posterior cranial fossa through the foramen magnum.
Innervation of the dura mater (Fig. 8.34) is by small meningeal branches of all three divisions of the trigeminal nerve [V1, V2, and V3], the vagus nerve [X], and the first, second, and, sometimes, third cervical nerves. (Possible involvement of the glossopharyngeal [IX] and hypoglossal nerves [XII] in the posterior cranial fossa has also been reported.)
In the anterior cranial fossa meningeal branches from the ethmoidal nerves, which are branches of the ophthalmic nerve [V1], supply the floor and the anterior part of the falx cerebri. |
Additionally, a meningeal branch of the ophthalmic nerve [V1] turns and runs posteriorly, supplying the tentorium cerebelli and the posterior part of the falx cerebri.
The middle cranial fossa is supplied medially by meningeal branches from the maxillary nerve [V2] and laterally, along the distribution of the middle meningeal artery, by meningeal branches from the mandibular nerve [V3].
The posterior cranial fossa is supplied by meningeal branches from the first, second, and, sometimes, third cervical nerves, which enter the fossa through the foramen magnum, the hypoglossal canal, and the jugular foramen. Meningeal branches of the vagus nerve [X] have also been described. (Possible contributions from the glossopharyngeal [IX] and hypoglossal [XII] nerves have also been reported.)
The arachnoid mater is a thin, avascular membrane that lines, but is not adherent to, the inner surface of the dura mater (Fig. 8.35). From its inner surface thin processes or trabeculae extend downward, cross the subarachnoid space, and become continuous with the pia mater.
Unlike the pia, the arachnoid does not enter the grooves or fissures of the brain, except for the longitudinal fissure between the two cerebral hemispheres.
The pia mater is a thin, delicate membrane that closely invests the surface of the brain (Fig. 8.35). It follows the contours of the brain, entering the grooves and fissures on its surface, and is closely applied to the roots of the cranial nerves at their origins.
Arrangement of meninges and spaces
There is a unique arrangement of meninges coupled with real and potential spaces within the cranial cavity (Fig. 8.35).
A potential space is related to the dura mater, while a real space exists between the arachnoid mater and the pia mater.
The potential space between dura mater and bone is the extradural space (Fig. 8.35). Normally, the outer or periosteal layer of dura mater is firmly attached to the bones surrounding the cranial cavity.
This potential space between dura and bone can become a fluid-filled actual space when a traumatic event results in a vascular hemorrhage. Bleeding into the extradural space primarily due to rupture of a meningeal artery or less often from a torn dural venous sinus results in an extradural hematoma.
Anatomically, a true subdural space does not exist. Blood collecting in this region (subdural hematoma) due to injury represents a dissection of the dural border cell layer, which is the innermost lining of the meningeal dura. Dural border cells are flattened cells surrounded by extracellular spaces filled with amorphous material. While very infrequent, an occasional cell junction may be seen between these cells and the underlying arachnoid layer. Bleeding due to the tearing of a cerebral vein as it crosses through the dura to enter a dural venous sinus can result in a subdural hematoma.
Deep to the arachnoid mater is the only normally occurring fluid-filled space associated with the meninges, the subarachnoid space (Fig. 8.35). It occurs because the arachnoid mater clings to the inner surface of the dura mater and does not follow the contour of the brain, while the pia mater, being against the surface of the brain, closely follows the grooves and fissures on the surface of the brain. The narrow subarachnoid space is therefore created between these two membranes (Fig. 8.35).
The subarachnoid space surrounds the brain and spinal cord and in certain locations it enlarges into expanded areas (subarachnoid cisterns). It contains cerebrospinal fluid (CSF) and blood vessels.
Cerebrospinal fluid is produced by the choroid plexus, primarily in the ventricles of the brain. It is a clear, colorless, cell-free fluid that circulates through the subarachnoid space surrounding the brain and spinal cord. |
The CSF returns to the venous system through arachnoid villi. These project as clumps (arachnoid granulations) into the superior sagittal sinus, which is a dural venous sinus, and its lateral extensions, the lateral lacunae (Fig. 8.35).
The brain is a component of the central nervous system.
During development the brain can be divided into five continuous parts (Figs. 8.36 and 8.37). From rostral (or cranial) to caudal they are:
The telencephalon (cerebrum) becomes the large cerebral hemispheres. The surface of these hemispheres consists of elevations (gyri) and depressions (sulci), and the hemispheres are partially separated by a deep longitudinal fissure. The cerebrum fills the area of the cranial cavity above the tentorium cerebelli and is subdivided into lobes based on position.
The diencephalon, which is hidden from view in the adult brain by the cerebral hemispheres, consists of the thalamus, hypothalamus, and other related structures, and classically is considered to be the most rostral part of the brainstem. (However, in common usage today, the term brainstem usually refers to the midbrain, pons, and medulla.)
The mesencephalon (midbrain), which is the first part of the brainstem seen when an intact adult brain is examined, spans the junction between the middle and posterior cranial fossae.
The metencephalon, which gives rise to the cerebellum (consisting of two lateral hemispheres and a midline part in the posterior cranial fossa below the tentorium cerebelli) and the pons (anterior to the cerebellum, and is a bulging part of the brainstem in the most anterior part of the posterior cranial fossa against the clivus and dorsum sellae).
The myelencephalon (medulla oblongata), the caudalmost part of the brainstem, ends at the foramen magnum or the uppermost rootlets of the first cervical nerve and to which cranial nerves VI to XII are attached.
The brain receives its arterial supply from two pairs of vessels, the vertebral and internal carotid arteries (Fig. 8.38), which are interconnected in the cranial cavity to produce a cerebral arterial circle (of Willis).
The two vertebral arteries enter the cranial cavity through the foramen magnum and just inferior to the pons fuse to form the basilar artery.
The two internal carotid arteries enter the cranial cavity through the carotid canals on either side.
Each vertebral artery arises from the first part of each subclavian artery (Fig. 8.38) in the lower part of the neck, and passes superiorly through the foramen transversarium of the upper six cervical vertebrae. On entering the cranial cavity through the foramen magnum each vertebral artery gives off a small meningeal branch.
Continuing forward, the vertebral artery gives rise to three additional branches before joining with its companion vessel to form the basilar artery (Figs. 8.38 and 8.39):
The first is a posterior inferior cerebellar artery.
A second branch is the posterior spinal artery, which passes posteriorly around the medulla and then descends on the posterior surface of the spinal cord in the area of the attachment of the posterior roots—there are two posterior spinal arteries, one on each side (although the posterior spinal arteries can originate directly from the vertebral arteries, they more commonly branch from the posterior inferior cerebellar arteries).
A third branch joins with its companion from the other side to form the single anterior spinal artery, which then descends in the anterior median fissure of the spinal cord. |
The basilar artery travels in a rostral direction along the anterior aspect of the pons (Fig. 8.39). Its branches in a caudal to rostral direction include the anterior inferior cerebellar arteries, several small pontine arteries, and the superior cerebellar arteries. The basilar artery ends as a bifurcation, giving rise to two posterior cerebral arteries.
The two internal carotid arteries arise as one of the two terminal branches of the common carotid arteries (Fig. 8.38). They proceed superiorly to the base of the skull where they enter the carotid canal.
Entering the cranial cavity each internal carotid artery gives off the ophthalmic artery, the posterior communicating artery, the middle cerebral artery, and the anterior cerebral artery (Fig. 8.39).
The cerebral arterial circle (of Willis) is formed at the base of the brain by the interconnecting vertebrobasilar and internal carotid systems of vessels (Fig. 8.38). This anastomotic interconnection is accomplished by: an anterior communicating artery connecting the left and right anterior cerebral arteries to each other, and two posterior communicating arteries, one on each side, connecting the internal carotid artery with the posterior cerebral artery (Figs. 8.38 and 8.39).
Venous drainage of the brain begins internally as networks of small venous channels lead to larger cerebral veins, cerebellar veins, and veins draining the brainstem, which eventually empty into dural venous sinuses. The dural venous sinuses are endothelial-lined spaces between the outer periosteal and the inner meningeal layers of the dura mater, and eventually lead to the internal jugular veins.
Also emptying into the dural venous sinuses are diploic veins, which run between the internal and external tables of compact bone in the roof of the cranial cavity, and emissary veins, which pass from outside the cranial cavity to the dural venous sinuses (Fig. 8.43).
The emissary veins are important clinically because they can be a conduit through which infections can enter the cranial cavity because they have no valves.
The dural venous sinuses include the superior sagittal, inferior sagittal, straight, transverse, sigmoid, and occipital sinuses, the confluence of sinuses, and the cavernous, sphenoparietal, superior petrosal, inferior petrosal, and basilar sinuses (Fig. 8.44, Table 8.3).
The superior sagittal sinus is in the superior border of the falx cerebri (Fig. 8.44). It begins anteriorly at the foramen cecum, where it may receive a small emissary vein from the nasal cavity, and ends posteriorly in the confluence of sinuses, usually bending to the right to empty into the right transverse sinus. The superior sagittal sinus communicates with lateral extensions (lateral lacunae) of the sinus containing numerous arachnoid granulations.
The superior sagittal sinus usually receives cerebral veins from the superior surface of the cerebral hemispheres, diploic and emissary veins, and veins from the falx cerebri.
The inferior sagittal sinus is in the inferior margin of the falx cerebri (Fig. 8.44). It receives a few cerebral veins and veins from the falx cerebri, and ends posteriorly at the anterior edge of the tentorium cerebelli, where it is joined by the great cerebral vein and together with the great cerebral vein forms the straight sinus (Fig. 8.44).
The straight sinus continues posteriorly along the junction of the falx cerebri and the tentorium cerebelli and ends in the confluence of sinuses, usually bending to the left to empty into the left transverse sinus. |
The straight sinus usually receives blood from the inferior sagittal sinus, cerebral veins (from the posterior part of the cerebral hemispheres), the great cerebral vein (draining deep areas of the cerebral hemispheres), superior cerebellar veins, and veins from the falx cerebri.
Confluence of sinuses, transverse and
The superior sagittal and straight sinuses, and the occipital sinus (in the falx cerebelli) empty into the confluence of sinuses, which is a dilated space at the internal occipital protuberance (Fig. 8.44) and is drained by the right and left transverse sinuses.
The paired transverse sinuses extend in horizontal directions from the confluence of sinuses where the tentorium cerebelli joins the lateral and posterior walls of the cranial cavity.
The right transverse sinus usually receives blood from the superior sagittal sinus and the left transverse sinus usually receives blood from the straight sinus.
The transverse sinuses also receive blood from the superior petrosal sinus, veins from the inferior parts of the cerebral hemispheres and the cerebellum, and diploic and emissary veins.
As the transverse sinuses leave the surface of the occipital bone, they become the sigmoid sinuses (Fig. 8.44), which turn inferiorly, grooving the parietal, temporal, and occipital bones, before ending at the beginning of the internal jugular veins. The sigmoid sinuses also receive blood from cerebral, cerebellar, diploic, and emissary veins.
The paired cavernous sinuses are against the lateral aspect of the body of the sphenoid bone on either side of the sella turcica (Figs. 8.45 and 8.46). They are of great clinical importance because of their connections and the structures that pass through them.
The cavernous sinuses receive blood not only from cerebral veins but also from the ophthalmic veins (from the orbit) and emissary veins (from the pterygoid plexus of veins in the infratemporal fossa). These connections provide pathways for infections to pass from extracranial sites into intracranial locations. In addition, because structures pass through the cavernous sinuses and are located in the walls of these sinuses they are vulnerable to injury due to inflammation.
Structures passing through each cavernous sinus are: the internal carotid artery, and the abducent nerve [VI].
Structures in the lateral wall of each cavernous sinus are, from superior to inferior: the oculomotor nerve [III], the trochlear nerve [IV], the ophthalmic nerve [V1], and the maxillary nerve [V2].
Connecting the right and left cavernous sinuses are the intercavernous sinuses on the anterior and posterior sides of the pituitary stalk (Fig. 8.44).
Sphenoparietal sinuses drain into the anterior ends of each cavernous sinus. These small sinuses are along the inferior surface of the lesser wings of the sphenoid and receive blood from the diploic and meningeal veins.
The superior petrosal sinuses drain the cavernous sinuses into the transverse sinuses. Each superior petrosal sinus begins at the posterior end of the cavernous sinus, passes posterolaterally along the superior margin of the petrous part of each temporal bone, and connects to the transverse sinus (Fig. 8.44). The superior petrosal sinuses also receive cerebral and cerebellar veins.
The inferior petrosal sinuses also begin at the posterior ends of the cavernous sinuses. These bilateral sinuses pass posteroinferiorly in a groove between the petrous part of the temporal bone and the basal part of the occipital bone, ending in the internal jugular veins. They assist in draining the cavernous sinuses and also receive blood from cerebellar veins and veins from the internal ear and brainstem. |
Basilar sinuses connect the inferior petrosal sinuses to each other and to the vertebral plexus of veins. They are on the clivus, just posterior to the sella turcica of the sphenoid bone (Fig. 8.44).
The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through foramina or fissures in the cranial cavity. All nerves except one, the accessory nerve [XI], originate from the brain.
In addition to having somatic and visceral components similar to those of spinal nerves, some cranial nerves also contain special sensory and motor components (Tables 8.4 and 8.5).
The special sensory components are associated with hearing, seeing, smelling, balancing, and tasting.
Special motor components include those that innervate skeletal muscles derived embryologically from the pharyngeal arches and not from somites.
In human embryology, six pharyngeal arches are designated, but the fifth pharyngeal arch never develops. Each of the pharyngeal arches that does develop is associated with a developing cranial nerve or one of its branches. These cranial nerves carry efferent fibers that innervate the musculature derived from the pharyngeal arch.
Innervation of the musculature derived from the five pharyngeal arches that do develop is as follows: first arch—trigeminal nerve [V3], second arch—facial nerve [VII], third arch—glossopharyngeal nerve [IX], fourth arch—superior laryngeal branch of the vagus nerve [X], sixth arch—recurrent laryngeal branch of the vagus nerve [X], posterior arches—accessory nerve [XI].
The olfactory nerve [I] carries special afferent (SA) fibers for the sense of smell. Its sensory neurons have: peripheral processes that act as receptors in the nasal mucosa, and central processes that return information to the brain.
The receptors are in the roof and upper parts of the nasal cavity, and the central processes, after joining into small bundles, enter the cranial cavity by passing through the cribriform plate of the ethmoid bone (Fig. 8.53). They terminate by synapsing with secondary neurons in the olfactory bulbs (Fig. 8.54).
The optic nerve [II] carries SA fibers for vision. These fibers return information to the brain from photoreceptors in the retina. Neuronal processes leave the retinal receptors, join into small bundles, and are carried by the optic nerves to other components of the visual system in the brain. The optic nerves enter the cranial cavity through the optic canals (Fig. 8.53).
The oculomotor nerve [III] carries two types of fibers:
General somatic efferent (GSE) fibers innervate most of the extra-ocular muscles.
General visceral efferent (GVE) fibers are part of the parasympathetic part of the autonomic division of the PNS.
The oculomotor nerve [III] leaves the anterior surface of the brainstem between the midbrain and the pons (Fig. 8.54). It enters the anterior edge of the tentorium cerebelli, continues in an anterior direction in the lateral wall of the cavernous sinus (Figs. 8.53 and 8.54; see Fig. 8.45), and leaves the cranial cavity through the superior orbital fissure.
In the orbit, the GSE fibers in the oculomotor nerve innervate levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique muscles.
The GVE fibers are preganglionic parasympathetic fibers that synapse in the ciliary ganglion and ultimately innervate the sphincter pupillae muscle, responsible for pupillary constriction, and the ciliary muscles, responsible for accommodation of the lens for near vision. |
The trochlear nerve [IV] is a cranial nerve that carries GSE fibers to innervate the superior oblique muscle, an extra-ocular muscle in the orbit. It arises in the midbrain and is the only cranial nerve to exit from the posterior surface of the brainstem (Fig. 8.54). After curving around the midbrain, it enters the inferior surface of the free edge of the tentorium cerebelli, continues in an anterior direction in the lateral wall of the cavernous sinus (Figs. 8.53 and 8.54; see Fig. 8.45), and enters the orbit through the superior orbital fissure.
The trigeminal nerve [V] is the major general sensory nerve of the head and also innervates muscles that move the lower jaw. It carries general somatic afferent (GSA) and branchial efferent (BE) fibers:
The GSA fibers provide sensory input from the face, anterior one-half of the scalp, mucous membranes of the oral and nasal cavities and the paranasal sinuses, the nasopharynx, part of the ear and external acoustic meatus, part of the tympanic membrane, the orbital contents and conjunctiva, and the dura mater in the anterior and middle cranial fossae.
The BE fibers innervate the muscles of mastication; the tensor tympani, tensor veli palatini, and mylohyoid muscles; and the anterior belly of the digastric muscle.
The trigeminal nerve exits from the anterolateral surface of the pons as a large sensory root and a small motor root (Fig. 8.54). These roots continue forward out of the posterior cranial fossa and into the middle cranial fossa by passing over the medial tip of the petrous part of the temporal bone (Fig. 8.53).
In the middle cranial fossa the sensory root expands into the trigeminal ganglion (Fig. 8.53), which contains cell bodies for the sensory neurons in the trigeminal nerve and is comparable to a spinal ganglion. The ganglion is in a depression (the trigeminal depression) on the anterior surface of the petrous part of the temporal bone, in a dural cave (the trigeminal cave). The motor root is below and completely separate from the sensory root at this point.
Arising from the anterior border of the trigeminal ganglion are the three terminal divisions of the trigeminal nerve, which in descending order are: the ophthalmic nerve (ophthalmic division [V1]).
the maxillary nerve (maxillary division [V2]), and the mandibular nerve (mandibular division [V3]).
The ophthalmic nerve [V1] passes forward in the dura of the lateral wall of the cavernous sinus (see Fig. 8.45), leaves the cranial cavity, and enters the orbit through the superior orbital fissure (Fig. 8.53).
The ophthalmic nerve [V1] carries sensory branches from the eyes, conjunctiva, and orbital contents, including the lacrimal gland. It also receives sensory branches from the nasal cavity, frontal sinus, ethmoidal cells, falx cerebri, dura in the anterior cranial fossa and superior parts of the tentorium cerebelli, upper eyelid, dorsum of the nose, and the anterior part of the scalp.
The maxillary nerve [V2] passes forward in the dura mater of the lateral wall of the cavernous sinus just inferior to the ophthalmic nerve [V1] (see Fig. 8.45), leaves the cranial cavity through the foramen rotundum (Fig. 8.53), and enters the pterygopalatine fossa. |
The maxillary nerve [V2] receives sensory branches from the dura in the middle cranial fossa, the nasopharynx, the palate, the nasal cavity, teeth of the upper jaw, maxillary sinus, and skin covering the side of the nose, the lower eyelid, the cheek, and the upper lip.
The mandibular nerve [V3] leaves the inferior margin of the trigeminal ganglion and leaves the skull through the foramen ovale (Fig. 8.53), and enters the infratemporal fossa.
The motor root of the trigeminal nerve also passes through the foramen ovale and unites with the sensory component of the mandibular nerve [V3] outside the skull. Thus the mandibular nerve [V3] is the only division of the trigeminal nerve that contains a motor component.
Outside the skull the motor fibers innervate the four muscles of mastication (temporalis, masseter, and medial and lateral pterygoids), as well as the tensor tympani muscle, the tensor veli palatini muscle, the anterior belly of the digastric muscle, and the mylohyoid muscle.
The mandibular nerve [V3] also receives sensory branches from the skin of the lower face, cheek, lower lip, anterior part of the external ear, part of the external acoustic meatus and the temporal region, the anterior two-thirds of the tongue, the teeth of the lower jaw, the mastoid air cells, the mucous membranes of the cheek, the mandible, and dura in the middle cranial fossa.
The abducent nerve [VI] carries GSE fibers to innervate the lateral rectus muscle in the orbit. It arises from the brainstem between the pons and medulla and passes forward, piercing the dura covering the clivus (Figs. 8.53 and 8.54). Continuing upward in a dural canal, it crosses the superior edge of the petrous part of the temporal bone, enters and crosses the cavernous sinus (see Fig. 8.45) just inferolateral to the internal carotid artery, and enters the orbit through the superior orbital fissure.
The facial nerve [VII] carries GSA, SA, GVE, and BE fibers:
The GSA fibers provide sensory input from part of the external acoustic meatus and deeper parts of the auricle.
The SA fibers are for taste from the anterior two-thirds of the tongue.
The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the lacrimal gland, submandibular and sublingual salivary glands, and glands in the mucous membranes of the nasal cavity, and hard and soft palates.
The BE fibers innervate the muscles of the face (muscles of facial expression) and scalp derived from the second pharyngeal arch, and the stapedius muscle, the posterior belly of the digastric muscle, and the stylohyoid muscle.
The facial nerve [VII] attaches to the lateral surface of the brainstem, between the pons and medulla oblongata (Fig. 8.54). It consists of a large motor root and a smaller sensory root (the intermediate nerve):
The intermediate nerve contains the SA fibers for taste, the parasympathetic GVE fibers, and the GSA fibers.
The larger motor root contains the BE fibers.
The motor and sensory roots cross the posterior cranial fossa and leave the cranial cavity through the internal acoustic meatus (Fig. 8.53). After entering the facial canal in the petrous part of the temporal bone, the two roots fuse and form the facial nerve [VII]. Near this point the nerve enlarges as the geniculate ganglion, which is similar to a spinal ganglion containing cell bodies for sensory neurons. |
At the geniculate ganglion the facial nerve [VII] turns and gives off the greater petrosal nerve, which carries mainly preganglionic parasympathetic (GVE) fibers (Table 8.6).
The facial nerve [VII] continues along the bony canal, giving off the nerve to the stapedius and the chorda tympani, before exiting the skull through the stylomastoid foramen.
The chorda tympani carries taste (SA) fibers from the anterior two-thirds of the tongue and preganglionic parasympathetic (GVE) fibers destined for the submandibular ganglion (Table 8.6).
The vestibulocochlear nerve [VIII] carries SA fibers for hearing and balance, and consists of two divisions: a vestibular component for balance, and a cochlear component for hearing.
The vestibulocochlear nerve [VIII] attaches to the lateral surface of the brainstem, between the pons and medulla, after emerging from the internal acoustic meatus and crossing the posterior cranial fossa (Figs. 8.53 and 8.54). The two divisions combine into the single nerve seen in the posterior cranial fossa within the substance of the petrous part of the temporal bone.
The glossopharyngeal nerve [IX] carries GVA, GSA, SA, GVE, and BE fibers:
The GVA fibers provide sensory input from the carotid body and sinus.
The GSA fibers provide sensory input from the posterior one-third of the tongue, palatine tonsils, oropharynx, and mucosa of the middle ear, pharyngotympanic tube, and mastoid air cells.
The SA fibers are for taste from the posterior one-third of the tongue.
The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the parotid salivary gland.
The BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle).
The glossopharyngeal nerve [IX] arises as several rootlets on the anterolateral surface of the upper medulla oblongata (Fig. 8.54). The rootlets cross the posterior cranial fossa and enter the jugular foramen (Fig. 8.53). Within the jugular foramen, and before exiting from it, the rootlets merge to form the glossopharyngeal nerve.
Within or immediately outside the jugular foramen are two ganglia (the superior and inferior ganglia), which contain the cell bodies of the sensory neurons in the glossopharyngeal nerve [IX].
Branching from the glossopharyngeal nerve [IX] either within or immediately outside the jugular foramen is the tympanic nerve. This branch reenters the temporal bone, enters the middle ear cavity, and participates in the formation of the tympanic plexus. Within the middle ear cavity it provides sensory innervation to the mucosa of the cavity, pharyngotympanic tube, and mastoid air cells.
The tympanic nerve also contributes GVE fibers, which leave the tympanic plexus in the lesser petrosal nerve—a small nerve that exits the temporal bone, enters the middle cranial fossa, and descends through the foramen ovale to exit the cranial cavity carrying preganglionic parasympathetic fibers to the otic ganglion (Table 8.6).
The vagus nerve [X] carries GSA, GVA, SA, GVE, and
BE fibers:
The GSA fibers provide sensory input from the larynx, laryngopharynx, deeper parts of the auricle, part of the external acoustic meatus, and the dura mater in the posterior cranial fossa.
The GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the esophagus, bronchi, lungs, heart, and abdominal viscera in the foregut and midgut. |
The SA fibers are for taste around the epiglottis and pharynx.
The GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut.
The BE fibers innervate one muscle of the tongue (palatoglossus), the muscles of the soft palate (except the tensor veli palatini), pharynx (except the stylopharyngeus), and larynx.
The vagus nerve arises as a group of rootlets on the anterolateral surface of the medulla oblongata just inferior to the rootlets arising to form the glossopharyngeal nerve [IX] (Fig. 8.54). The rootlets cross the posterior cranial fossa and enter the jugular foramen (Fig. 8.53). Within this foramen, and before exiting from it, the rootlets merge to form the vagus nerve [X]. Within or immediately outside the jugular foramen are two ganglia, the superior (jugular) and inferior (nodose) ganglia, which contain the cell bodies of the sensory neurons in the vagus nerve [X].
The accessory nerve [XI] is a cranial nerve that carries BE fibers to innervate the sternocleidomastoid and trapezius muscles (see Diogo R et al. Nature 2015;520:466–473). It is a unique cranial nerve because its roots arise from motor neurons in the upper five segments of the cervical spinal cord. These fibers leave the lateral surface of the spinal cord and, joining together as they ascend, enter the cranial cavity through the foramen magnum (Fig. 8.54). The accessory nerve [XI] continues through the posterior cranial fossa and exits through the jugular foramen (Fig. 8.53). It then descends in the neck to innervate the sternocleidomastoid and trapezius muscles from their deep surfaces.
Cranial root of the accessory nerve
Some descriptions of the accessory nerve [XI] refer to a few rootlets arising from the caudal part of the medulla oblongata on the anterolateral surface just inferior to the rootlets arising to form the vagus nerve [X] as the “cranial” root of the accessory nerve (Fig. 8.54). Leaving the medulla, the cranial roots course with the “spinal” roots of the accessory nerve [XI] into the jugular foramen, at which point the cranial roots join the vagus nerve [X]. As part of the vagus nerve [X], they are distributed to the pharyngeal musculature innervated by the vagus nerve [X] and are therefore described as being part of the vagus nerve [X].
The hypoglossal nerve [XII] carries GSE fibers to innervate all intrinsic muscles and most of the extrinsic muscles of the tongue. It arises as several rootlets from the anterior surface of the medulla (Fig. 8.54), passes laterally across the posterior cranial fossa, and exits through the hypoglossal canal (Fig. 8.53). This nerve innervates the hyoglossus, styloglossus, and genioglossus muscles and all intrinsic muscles of the tongue.
A face-to-face meeting is an important initial contact between individuals. Part of this exchange is the use of facial expressions to convey emotions. In fact, a physician can gain important information about an individual’s general health by observing a patient’s face.
Thus an understanding of the unique organization of the various structures between the superciliary arches superiorly, the lower edge of the mandible inferiorly, and as far back as the ears on either side, the area defined as the face, is particularly useful in the practice of medicine. |
The muscles of the face (Fig. 8.56) develop from the second pharyngeal arch and are innervated by branches of the facial nerve [VII]. They are in the superficial fascia, with origins from either bone or fascia, and insertions into the skin.
Because these muscles control expressions of the face, they are sometimes referred to as muscles of “facial expression.” They also act as sphincters and dilators of the orifices of the face (i.e., the orbits, nose, and mouth). This organizational arrangement into functional groups provides a logical approach to understanding these muscles (Table 8.7).
Two muscles are associated with the orbital group—the orbicularis oculi and the corrugator supercilii.
The orbicularis oculi is a large muscle that completely surrounds each orbital orifice and extends into each eyelid (Fig. 8.57). It closes the eyelids. It has two major parts:
The outer orbital part is a broad ring that encircles the orbital orifice and extends outward beyond the orbital rim.
The inner palpebral part is in the eyelids and consists of muscle fibers originating in the medial corner of the eye that arch across each lid to attach laterally.
The orbital and palpebral parts have specific roles to play during eyelid closure. The palpebral part closes the eye gently, whereas the orbital part closes the eye more forcefully and produces some wrinkling on the forehead.
An additional small lacrimal part of the orbicularis oculi muscle is deep, medial in position, and attaches to bone posterior to the lacrimal sac of the lacrimal apparatus in the orbit.
The second muscle in the orbital group is the much smaller corrugator supercilii (Fig. 8.57), which is deep to the eyebrows and the orbicularis oculi muscle and is active when frowning. It arises from the medial end of the superciliary arch, passing upward and laterally to insert into the skin of the medial half of the eyebrow. It draws the eyebrows toward the midline, causing vertical wrinkles above the nose.
Three muscles are associated with the nasal group—the nasalis, the procerus, and the depressor septi nasi (Fig. 8.58).
The largest and best developed of the muscles of the nasal group is the nasalis, which is active when the nares are flared (Fig. 8.58). It consists of a transverse part (the compressor naris) and an alar part (the dilator naris):
The transverse part of the nasalis compresses the nares—it originates from the maxilla and its fibers pass upward and medially to insert, along with fibers from the same muscle on the opposite side, into an aponeurosis across the dorsum of the nose.
The alar part of the nasalis draws the alar cartilages downward and laterally, so opening the nares—it originates from the maxilla, below and medial to the transverse part, and inserts into the alar cartilage.
The procerus is a small muscle superficial to the nasal bone and is active when an individual frowns (Fig. 8.58). It arises from the nasal bone and the upper part of the lateral nasal cartilage and inserts into the skin over the lower part of the forehead between the eyebrows. It may be continuous with the frontal belly of the occipitofrontalis muscle of the scalp.
The procerus draws the medial border of the eyebrows downward to produce transverse wrinkles over the bridge of the nose.
The final muscle in the nasal group is the depressor septi nasi, another muscle that assists in widening the nares (Fig. 8.58). Its fibers arise from the maxilla above the central incisor tooth and ascend to insert into the lower part of the nasal septum.
The depressor septi nasi pulls the nose inferiorly, so assisting the alar part of the nasalis in opening the nares. |
The muscles in the oral group move the lips and cheek. They include the orbicularis oris and buccinator muscles, and a lower and upper group of muscles (Fig. 8.59). Many of these muscles intersect just lateral to the corner of the mouth on each side at a structure termed the modiolus.
The orbicularis oris is a complex muscle consisting of fibers that completely encircle the mouth (Fig. 8.59). Its function is apparent when pursing the lips, as occurs during whistling. Some of its fibers originate near the midline from the maxilla superiorly and the mandible inferiorly, whereas other fibers are derived from both the buccinator, in the cheek, and the numerous other muscles acting on the lips. It inserts into the skin and mucous membrane of the lips, and into itself.
Contraction of the orbicularis oris narrows the mouth and closes the lips.
The buccinator forms the muscular component of the cheek and is used every time air expanding the cheeks is forcefully expelled (Figs. 8.59 and 8.60). It is in the space between the mandible and the maxilla, deep to the other facial muscles in the area.
The buccinator arises from the posterior part of the maxilla and mandible opposite the molar teeth and the pterygomandibular raphe, which is a tendinous band between the pterygoid hamulus superiorly and the mandible inferiorly and is a point of attachment for the buccinator and superior pharyngeal constrictor muscles.
The fibers of the buccinator pass toward the corner of the mouth to insert into the lips, blending with fibers from the orbicularis oris in a unique fashion. Central fibers of the buccinator cross so that lower fibers enter the upper lip and upper fibers enter the lower lip (Fig. 8.60). The highest and lowest fibers of the buccinator do not cross and enter the upper and lower lips, respectively.
Contraction of the buccinator presses the cheek against the teeth. This keeps the cheek taut and aids in mastication by preventing food from accumulating between the teeth and the cheek. The muscle also assists in the forceful expulsion of air from the cheeks.
Lower group of oral muscles
The muscles in the lower group consist of the depressor anguli oris, depressor labii inferioris. and mentalis (Fig. 8.59).
The depressor anguli oris is active during frowning.
It arises along the side of the mandible below the canine, premolar, and first molar teeth and inserts into skin and the upper part of the orbicularis oris near the corner of the mouth. It depresses the corner of the mouth.
The depressor labii inferioris arises from the front of the mandible, deep to the depressor anguli oris. Its fibers move superiorly and medially, some merging with fibers from the same muscle on the opposite side and fibers from the orbicularis oris before inserting into the lower lip. It depresses the lower lip and moves it laterally.
The mentalis helps position the lip when drinking from a cup or when pouting. It is the deepest muscle of the lower group arising from the mandible just inferior to the incisor teeth, with its fibers passing downward and medially to insert into the skin of the chin. It raises and protrudes the lower lip as it wrinkles the skin of the chin.
Upper group of oral muscles
The muscles of the upper group of oral muscles consist of the risorius, zygomaticus major, zygomaticus minor, levator labii superioris, levator labii superioris alaeque nasi, and levator anguli oris (Fig. 8.59).
The risorius helps produce a grin (Fig. 8.59). It is a thin, superficial muscle that extends laterally from the corner of the mouth in a slightly upward direction. Contraction of its fibers pulls the corner of the mouth laterally and upward. |
The zygomaticus major and zygomaticus minor help produce a smile (Fig. 8.59). The zygomaticus major is a superficial muscle that arises deep to the orbicularis oculi along the posterior part of the lateral surface of the zygomatic bone, and passes downward and forward, blending with the orbicularis oris and inserting into skin at the corner of the mouth. The zygomaticus minor arises from the zygomatic bone anterior to the origin of the zygomaticus major, parallels the path of the zygomaticus major, and inserts into the upper lip medial to the corner of the mouth. Both zygomaticus muscles raise the corner of the mouth and move it laterally.
The levator labii superioris deepens the furrow between the nose and the corner of the mouth during sadness (Fig. 8.59). It arises from the maxilla just superior to the infra-orbital foramen, and its fibers pass downward and medially to blend with the orbicularis oris and insert into the skin of the upper lip.
The levator labii superioris alaeque nasi is medial to the levator labii superioris, arises from the maxilla next to the nose, and inserts into both the alar cartilage of the nose and skin of the upper lip (Fig. 8.59). It may assist in flaring the nares.
The levator anguli oris is more deeply placed and covered by the other two levators and the zygomaticus muscles (Fig. 8.59). It arises from the maxilla, just inferior to the infra-orbital foramen and inserts into the skin at the corner of the mouth. It elevates the corner of the mouth and may help deepen the furrow between the nose and the corner of the mouth during sadness.
Several additional muscles or groups of muscles not in the area defined as the face, but derived from the second pharyngeal arch and innervated by the facial nerve [VII], are considered muscles of facial expression. They include the platysma, auricular, and occipitofrontalis muscles (see Fig. 8.56).
The platysma is a large, thin sheet of muscle in the superficial fascia of the neck. It arises below the clavicle in the upper part of the thorax and ascends through the neck to the mandible. At this point, the more medial fibers insert on the mandible, whereas the lateral fibers join with muscles around the mouth.
The platysma tenses the skin of the neck and can move the lower lip and corners of the mouth down.
Three of these muscles, “other muscles of facial expression,” are associated with the ear—the anterior, superior, and posterior auricular muscles (Fig. 8.61):
The anterior muscle is anterolateral and pulls the ear upward and forward.
The superior muscle is superior and elevates the ear.
The posterior muscle is posterior and retracts and elevates the ear.
The occipitofrontalis is the final muscle in this category of “other muscles of facial expression” and is associated with the scalp (see Fig. 8.56). It consists of a frontal belly anteriorly and an occipital belly posteriorly. An aponeurotic tendon connects the two:
The frontal belly covers the forehead and is attached to the skin of the eyebrows.
The occipital belly arises from the posterior aspect of the skull and is smaller than the frontal belly.
The occipitofrontalis muscles move the scalp and wrinkle the forehead.
The parotid glands are the largest of the three pairs of main salivary glands in the head and numerous structures pass through them. They are anterior to and below the lower half of the ear, superficial, posterior, and deep to the ramus of the mandible (Fig. 8.62). They extend down to the lower border of the mandible and up to the zygomatic arch. Posteriorly they cover the anterior part of the sternocleidomastoid muscle and continue anteriorly to halfway across the masseter muscle. |
The parotid duct leaves the anterior edge of the parotid gland midway between the zygomatic arch and the corner of the mouth (Fig. 8.62). It crosses the face in a transverse direction and, after crossing the medial border of the masseter muscle, turns deeply into the buccal fat pad and pierces the buccinator muscle. It opens into the oral cavity near the second upper molar tooth.
pass just deep to the parotid gland. These include the facial nerve [VII], the external carotid artery and its branches, and the retromandibular vein and its tributaries (Fig. 8.62).
The facial nerve [VII] exits the skull through the stylomastoid foramen and then passes into the parotid gland, where it usually divides into upper and lower trunks. These pass through the substance of the parotid gland, where there may be further branching and anastomosing of the nerves.
Five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal mandibular, and cervical branches—emerge from the upper, anterior, and lower borders of the parotid gland (Fig. 8.62).
The intimate relationships between the facial nerve [VII] and the parotid gland mean that surgical removal of the parotid gland is a difficult dissection if all branches of the facial nerve [VII] are to be spared.
The external carotid artery enters into or passes deep to the inferior border of the parotid gland (Fig. 8.62). As it continues in a superior direction, it gives off the posterior auricular artery before dividing into its two terminal branches (the maxillary and superficial temporal arteries) near the lower border of the ear:
The maxillary artery passes horizontally, deep to the mandible.
The superficial temporal artery continues in a superior direction and emerges from the upper border of the gland after giving off the transverse facial artery.
The retromandibular vein is formed in the substance of the parotid gland when the superficial temporal and maxillary veins join together (Fig. 8.62), and passes inferiorly in the substance of the parotid gland. It usually divides into anterior and posterior branches just below the inferior border of the gland.
The parotid gland receives its arterial supply from the numerous arteries that pass through its substance.
Sensory innervation of the parotid gland is provided by the auriculotemporal nerve, which is a branch of the mandibular nerve [V3]. This division of the trigeminal nerve exits the skull through the foramen ovale.
The auriculotemporal nerve also carries secretomotor fibers to the parotid gland. These postganglionic parasympathetic fibers have their origin in the otic ganglion associated with the mandibular nerve [V3] and are just inferior to the foramen ovale. Preganglionic parasympathetic fibers to the otic ganglion come from the glossopharyngeal nerve [IX].
During development a cranial nerve becomes associated with each of the pharyngeal arches. Because the face is primarily derived from the first and second pharyngeal arches, innervation of neighboring facial structures is as follows:
The trigeminal nerve [V] innervates facial structures derived from the first arch.
The facial nerve [VII] innervates facial structures derived from the second arch.
Because the face is derived developmentally from a number of structures originating from the first pharyngeal arch, cutaneous innervation of the face is by branches of the trigeminal nerve [V]. |
The trigeminal nerve [V] divides into three major divisions— the ophthalmic [V1], maxillary [V2], and mandibular [V3]—before leaving the middle cranial fossa (Fig. 8.64). Each of these divisions passes out of the cranial cavity to innervate a part of the face, so most of the skin covering the face is innervated solely by branches of the trigeminal nerve [V]. The exception is a small area covering the angle and lower border of the ramus of the mandible and parts of the ear, where the facial [VII], vagus [X], and cervical nerves contribute to the innervation.
The ophthalmic nerve [V1] exits the skull through the superior orbital fissure and enters the orbit. Its branches (Fig. 8.64) that innervate the face include: the supra-orbital and supratrochlear nerves, which leave the orbit superiorly and innervate the upper eyelid, forehead, and scalp; the infratrochlear nerve, which exits the orbit in the medial angle to innervate the medial half of the upper eyelid, the skin in the area of the medial angle, and the side of the nose; the lacrimal nerve, which exits the orbit in the lateral angle to innervate the lateral half of the upper eyelid and the skin in the area of the lateral angle; and the external nasal nerve, which supplies the anterior part of the nose (Fig. 8.65).
The maxillary nerve [V2] exits the skull through the foramen rotundum. Branches (Fig. 8.64) that innervate the face include: a small zygomaticotemporal branch, which exits the zygomatic bone and supplies a small area of the anterior temple above the zygomatic arch; a small zygomaticofacial branch, which exits the zygomatic bone and supplies a small area of skin over the zygomatic bone; and the large infra-orbital nerve, which exits the maxilla through the infra-orbital foramen and immediately divides into multiple branches to supply the lower eyelid, cheek, side of the nose, and upper lip (Fig. 8.65).
The mandibular nerve [V3] exits the skull through the foramen ovale. Branches (Fig. 8.65) innervating the face include: the auriculotemporal nerve, which enters the face just posterior to the temporomandibular joint, passes through the parotid gland, and ascends just anterior to the ear to supply the external acoustic meatus, the surface of the tympanic membrane (eardrum), and a large area of the temple; the buccal nerve, which is on the surface of the buccinator muscle supplying the cheek; and the mental nerve, which exits the mandible through the mental foramen and immediately divides into multiple branches to supply the skin and mucous membrane of the lower lip and skin of the chin (Fig. 8.65).
The muscles of the face, as well as those associated with the external ear and the scalp, are derived from the second pharyngeal arch. The cranial nerve associated with this arch is the facial nerve [VII] and therefore branches of the facial nerve [VII] innervate all these muscles.
The facial nerve [VII] exits the posterior cranial fossa through the internal acoustic meatus. It passes through the temporal bone, giving off several branches, and emerges from the base of the skull through the stylomastoid foramen (Fig. 8.66). At this point it gives off the posterior auricular nerve. This branch passes upward, behind the ear, to supply the occipital belly of the occipitofrontalis muscle of the scalp and the posterior auricular muscle of the ear. |
The main stem of the facial nerve [VII] then gives off another branch, which innervates the posterior belly of the digastric muscle and the stylohyoid muscle. At this point, the facial nerve [VII] enters the deep surface of the parotid gland (Fig. 8.66B).
Once in the parotid gland, the main stem of the facial nerve [VII] usually divides into upper (temporofacial) and lower (cervicofacial) branches. As these branches pass through the substance of the parotid gland they may branch further or take part in an anastomotic network (the parotid plexus).
Whatever types of interconnections occur, five terminal groups of branches of the facial nerve [VII]—the temporal, zygomatic, buccal, marginal mandibular, and cervical branches—emerge from the parotid gland (Fig. 8.66A).
Although there are variations in the pattern of distribution of the five terminal groups of branches, the basic pattern is as follows:
Temporal branches exit from the superior border of the parotid gland to supply muscles in the area of the temple, forehead, and supra-orbital area.
Zygomatic branches emerge from the anterosuperior border of the parotid gland to supply muscles in the infra-orbital area, the lateral nasal area, and the upper lip.
Buccal branches emerge from the anterior border of the parotid gland to supply muscles in the cheek, the upper lip, and the corner of the mouth.
Marginal mandibular branches emerge from the anteroinferior border of the parotid gland to supply muscles of the lower lip and chin.
Cervical branches emerge from the inferior border of the parotid gland to supply the platysma.
The arterial supply to the face is primarily from branches of the external carotid artery, though there is some limited supply from a branch of the internal carotid artery.
Similarly, most of the venous return is back to the internal jugular vein, though some important connections from the face result in venous return through a clinically relevant intracranial pathway involving the cavernous sinus.
The facial artery is the major vessel supplying the face (Fig. 8.67). It branches from the anterior surface of the external carotid artery, passes up through the deep structures of the neck, and appears at the lower border of the mandible after passing posterior to the submandibular gland. Curving around the inferior border of the mandible just anterior to the masseter, where its pulse can be felt, the facial artery then enters the face. From this point the facial artery runs upward and medially in a tortuous course. It passes along the side of the nose and terminates as the angular artery at the medial corner of the eye.
Along its path the facial artery is deep to the platysma, risorius, and zygomaticus major and minor, superficial to the buccinator and levator anguli oris, and may pass superficially to or through the levator labii superioris.
Branches of the facial artery include the superior and inferior labial branches and the lateral nasal branch (Fig. 8.67).
The labial branches arise near the corner of the mouth:
The inferior labial branch supplies the lower lip.
The superior labial branch supplies the upper lip, and also provides a branch to the nasal septum.
Near the midline, the superior and inferior labial branches anastomose with their companion arteries from the opposite side of the face. This provides an important connection between the facial arteries and the external carotid arteries of opposite sides.
The lateral nasal branch is a small branch arising from the facial artery as it passes along the side of the nose. It supplies the lateral surface and dorsum of the nose.
Another contributor to the vascular supply of the face is the transverse facial artery (Fig. 8.67), which is a branch of the superficial temporal artery (the smaller of the two terminal branches of the external carotid artery). |
The transverse facial artery arises from the superficial temporal artery within the substance of the parotid gland, passes through the gland, and crosses the face in a transverse direction. Lying on the superficial surface of the masseter muscle, it is between the zygomatic arch and the parotid duct.
Branches of the maxillary artery
The maxillary artery, the larger of the two terminal branches of the external carotid artery, gives off several small branches which contribute to the arterial supply to the face:
The infra-orbital artery enters the face through the infra-orbital foramen and supplies the lower eyelid, upper lip, and the area between these structures.
The buccal artery enters the face on the superficial surface of the buccinator muscle and supplies structures in this area.
The mental artery enters the face through the mental foramen and supplies the chin.
Branches of the ophthalmic artery
Three small arteries from the internal carotid artery also contribute to the arterial supply of the face. These vessels arise from the ophthalmic artery, a branch of the internal carotid artery, after the ophthalmic artery enters the orbit:
The zygomaticofacial and zygomaticotemporal arteries come from the lacrimal branch of the ophthalmic artery (Fig. 8.67), enter the face through the zygomaticofacial and zygomaticotemporal foramina, and supply the area of the face over the zygomatic bone.
The dorsal nasal artery, a terminal branch of the ophthalmic artery, exits the orbit in the medial corner, and supplies the dorsum of the nose.
The supraorbital and supratrochlear arteries supply the anterior scalp.
The facial vein is the major vein draining the face (Fig. 8.67). Its point of origin is near the medial corner of the orbit as the supratrochlear and supra-orbital veins come together to form the angular vein. This vein becomes the facial vein as it proceeds inferiorly and assumes a position just posterior to the facial artery. The facial vein descends across the face with the facial artery until it reaches the inferior border of the mandible. Here the artery and vein part company and the facial vein passes superficial to the submandibular gland to enter the internal jugular vein.
Throughout its course the facial vein receives tributaries from veins draining the eyelids, external nose, lips, cheek, and chin that accompany the various branches of the facial artery.
The transverse facial vein is a small vein that accompanies the transverse facial artery in its journey across the face (Fig. 8.67). It empties into the superficial temporal vein within the substance of the parotid gland.
As it crosses the face, the facial vein has numerous connections with venous channels passing into deeper regions of the head (Fig. 8.68): near the medial corner of the orbit, it communicates with ophthalmic veins; in the area of the cheek it communicates with veins passing into the infra-orbital foramen; it also communicates with veins passing into deeper regions of the face (i.e., the deep facial vein connecting with the pterygoid plexus of veins).
All these venous channels have interconnections with the intracranial cavernous sinus through emissary veins that connect intracranial with extracranial veins. There are no valves in the facial vein or any other venous channels in the head, so blood can move in any direction. Because of the interconnections between the veins, infections of the face, primarily above the mouth (i.e., the “danger area”) should be handled with great care to prevent the dissemination of infectious material in an intracranial direction. |
Lymphatic drainage from the face primarily moves toward three groups of lymph nodes (Fig. 8.69): submental nodes inferior and posterior to the chin, which drain lymphatics from the medial part of the lower lip and chin bilaterally; submandibular nodes superficial to the submandibular gland and inferior to the body of the mandible, which drain the lymphatics from the medial corner of the orbit, most of the external nose the medial part of the cheek, the upper lip, and the lateral part of the lower lip that follows the course of the facial artery; pre-auricular and parotid nodes anterior to the ear, which drain lymphatics from most of the eyelids, a part of the external nose, and the lateral part of the cheek.
The scalp is the part of the head that extends from the superciliary arches anteriorly to the external occipital protuberance and superior nuchal lines posteriorly. Laterally it continues inferiorly to the zygomatic arch.
The scalp is a multilayered structure with layers that can be defined by the word itself:
S—skin,
C—connective tissue (dense),
A—aponeurotic layer,
L—loose connective tissue, and
P—pericranium (Fig. 8.70).
Examining the layers of the scalp reveals that the first three layers are tightly held together, forming a single unit. This unit is sometimes referred to as the scalp proper and is the tissue torn away during serious “scalping” injuries.
The skin is the outer layer of the scalp (Figs. 8.70 and 8.71). It is similar structurally to skin throughout the body with the exception that hair is present on a large amount of it.
Deep to the skin is dense connective tissue. This layer anchors the skin to the third layer and contains the arteries, veins, and nerves supplying the scalp. When the scalp is cut, the dense connective tissue surrounding the vessels tends to hold cut vessels open. This results in profuse bleeding.
The deepest layer of the first three layers is the aponeurotic layer. Firmly attached to the skin by the dense connective tissue of the second layer, this layer consists of the occipitofrontalis muscle, which has a frontal belly anteriorly, an occipital belly posteriorly, and an aponeurotic tendon— the epicranial aponeurosis (galea aponeurotica)—connecting the two (Fig. 8.72).
The frontal belly of the occipitofrontalis begins anteriorly where it is attached to the skin of the eyebrows. It passes upward, across the forehead, to become continuous with the aponeurotic tendon.
Posteriorly, each occipital belly of the occipitofrontalis arises from the lateral part of the superior nuchal line of the occipital bone and the mastoid process of the temporal bone. It also passes superiorly to attach to the aponeurotic tendon.
The occipitofrontalis muscles move the scalp, wrinkle the forehead, and raise the eyebrows. The frontal belly is innervated by temporal branches of the facial nerve [VII] and the posterior belly by the posterior auricular branch.
A layer of loose connective tissue separates the aponeurotic layer from the pericranium and facilitates movement of the scalp proper over the calvaria (Figs. 8.70 and 8.72). Because of its consistency, infections tend to localize and spread through the loose connective tissue (also see “In the clinic” on p. 878).
The pericranium is the deepest layer of the scalp and is the periosteum on the outer surface of the calvaria. It is attached to the bones of the calvaria but is removable, except in the area of the sutures. |
Sensory innervation of the scalp is from two major sources, cranial nerves or cervical nerves, depending on whether it is anterior or posterior to the ears and the vertex of the head (Fig. 8.73), The occipitofrontalis muscle is innervated by branches of the facial nerve [VII].
Anterior to the ears and the vertex
Branches of the trigeminal nerve [V] supply the scalp anterior to the ears and the vertex of the head (Fig. 8.73). These branches are the supratrochlear, supra-orbital, zygomaticotemporal, and auriculotemporal nerves:
The supratrochlear nerve exits the orbit, passes through the frontalis muscle, continues superiorly across the front of the forehead, and supplies the front of the forehead near the midline.
The supra-orbital nerve exits the orbit through the supra-orbital notch or foramen, passes through the frontalis muscle, and continues superiorly across the scalp as far back as the vertex of the head.
The zygomaticotemporal nerve exits the skull through a foramen in the zygomatic bone and supplies the scalp over a small anterior area of the temple.
The auriculotemporal nerve exits from the skull, deep to the parotid gland, passes just anterior to the ear, continues superiorly anterior to the ear until nearly reaching the vertex of the head, and supplies the scalp over the temporal region and anterior to the ear to near the vertex.
Posterior to the ears and the vertex
Posterior to the ears and vertex, sensory innervation of the scalp is by cervical nerves, specifically branches from spinal cord levels C2 and C3 (Fig. 8.73). These branches are the great auricular, the lesser occipital, the greater occipital, and the third occipital nerves:
The great auricular nerve is a branch of the cervical plexus, arises from the anterior rami of the C2 and C3 spinal nerves, ascends on the surface of the sternocleidomastoid muscle, and innervates a small area of the scalp just posterior to the ear.
The lesser occipital nerve is also a branch of the cervical plexus, arises from the anterior ramus of the C2 spinal nerve, ascends on the posterior border of the sternocleidomastoid muscle, and supplies an area of the scalp posterior and superior to the ear.
The greater occipital nerve is a branch of the posterior ramus of the C2 spinal nerve, emerges just inferior to the obliquus capitis inferior muscle, ascends superficial to the suboccipital triangle, pierces the semispinalis capitis and trapezius muscles, and then spreads out to supply a large part of the posterior scalp as far superiorly as the vertex.
The third occipital nerve is a branch of the posterior ramus of the C3 spinal nerve, pierces the semispinalis capitis and trapezius muscles, and supplies a small area of the lower part of the scalp.
Arteries supplying the scalp (Fig. 8.74) are branches of either the external carotid artery or the ophthalmic artery, which is a branch of the internal carotid artery.
Branches from the ophthalmic artery
The supratrochlear and supra-orbital arteries supply the anterior and superior aspects of the scalp. They branch from the ophthalmic artery while it is in the orbit, continue through the orbit, and exit onto the forehead in association with the supratrochlear and supra-orbital nerves. Like the nerves, the arteries ascend across the forehead to supply the scalp as far posteriorly as the vertex of the head.
Branches from the external carotid artery
Three branches of the external carotid artery supply the largest part of the scalp—the superficial temporal, posterior auricular, and occipital arteries supply the lateral and posterior aspects of the scalp (Fig. 8.74):
The smallest branch (the posterior auricular artery) leaves the posterior aspect of the external carotid artery, passes through deeper structures, and emerges to supply an area of the scalp posterior to the ear. |
Also arising from the posterior aspect of the external carotid artery is the occipital artery, which ascends in a posterior direction, passes through several layers of back musculature, and emerges to supply a large part of the posterior aspect of the scalp.
The third arterial branch supplying the scalp is the superficial temporal artery, a terminal branch of the external carotid artery that passes superiorly, just anterior to the ear, divides into anterior and posterior branches, and supplies almost the entire lateral aspect of the scalp.
Veins draining the scalp follow a pattern similar to the arteries:
The supratrochlear and supra-orbital veins drain the anterior part of the scalp from the superciliary arches to the vertex of the head (Fig. 8.74), pass inferior to the superciliary arches, communicate with the ophthalmic veins in the orbit, and continue inferiorly to participate in the formation of the angular vein, which is the upper tributary to the facial vein.
The superficial temporal vein drains the entire lateral area of the scalp before passing inferiorly to join in the formation of the retromandibular vein.
The posterior auricular vein drains the area of the scalp posterior to the ear and eventually empties into a tributary of the retromandibular vein.
The occipital vein drains the posterior aspect of the scalp from the external occipital protuberance and superior nuchal lines to the vertex of the head; deeper, it passes through the musculature in the posterior neck to join in the formation of the plexus of veins in the suboccipital triangle.
Lymphatic drainage of the scalp generally follows the pattern of arterial distribution.
The lymphatics in the occipital region initially drain to occipital nodes near the attachment of the trapezius muscle at the base of the skull (Fig. 8.75). Further along the pathway occipital nodes drain into upper deep cervical nodes. There is also some direct drainage to upper deep cervical nodes from this part of the scalp.
Lymphatics from the upper part of the scalp drain in two directions:
Posterior to the vertex of the head they drain to mastoid nodes (retro-auricular/posterior auricular nodes) posterior to the ear near the mastoid process of the temporal bone, and efferent vessels from these nodes drain into upper deep cervical nodes.
Anterior to the vertex of the head they drain to pre-auricular and parotid nodes anterior to the ear on the surface of the parotid gland.
Finally, there may be some lymphatic drainage from the forehead to the submandibular nodes through efferent vessels that follow the facial artery.
The orbits are bilateral structures in the upper half of the face below the anterior cranial fossa and anterior to the middle cranial fossa that contain the eyeball, the optic nerve, the extra-ocular muscles, the lacrimal apparatus, adipose tissue, fascia, and the nerves and vessels that supply these structures.
Seven bones contribute to the framework of each orbit (Fig. 8.76). They are the maxilla, zygomatic, frontal, ethmoid, lacrimal, sphenoid, and palatine bones. Together they give the bony orbit the shape of a pyramid, with its wide base opening anteriorly onto the face and its apex extending in a posteromedial direction. Completing the pyramid configuration are medial, lateral, superior, and inferior walls.
The apex of the pyramid-shaped bony orbit is the optic foramen, whereas the base (the orbital rim) is formed: superiorly by the frontal bone, medially by the frontal process of the maxilla, inferiorly by the zygomatic process of the maxilla and the zygomatic bone, and laterally by the zygomatic bone, the frontal process of the zygomatic bone, and the zygomatic process of the frontal bone. |
The roof (superior wall) of the bony orbit is made up of the orbital part of the frontal bone with a small contribution from the sphenoid bone (Fig. 8.76). This thin plate of bone separates the contents of the orbit from the brain in the anterior cranial fossa.
Unique features of the superior wall include: anteromedially, the trochlear fovea, for the attachment of a pulley through which the superior oblique muscle passes, and the possible intrusion of part of the frontal sinus; anterolaterally, a depression (the lacrimal fossa) for the orbital part of the lacrimal gland.
Posteriorly, the lesser wing of the sphenoid bone completes the roof.
The medial walls of the paired bony orbits are parallel to each other and each consists of four bones—the maxilla, lacrimal, ethmoid, and sphenoid bones (Fig. 8.76).
The largest contributor to the medial wall is the orbital plate of the ethmoid bone. This part of the ethmoid bone contains collections of ethmoidal cells, which are clearly visible in a dried skull.
Also visible, at the junction between the roof and the medial wall, usually associated with the frontoethmoidal suture, are the anterior and posterior ethmoidal foramina. The anterior and posterior ethmoidal nerves and vessels leave the orbit through these openings.
Anterior to the ethmoid bone is the small lacrimal bone, and completing the anterior part of the medial wall is the frontal process of the maxilla. These two bones participate in the formation of the lacrimal groove, which contains the lacrimal sac and is bound by the posterior lacrimal crest (part of the lacrimal bone) and the anterior lacrimal crest (part of the maxilla).
Posterior to the ethmoid bone the medial wall is completed by a small part of the sphenoid bone, which forms a part of the medial wall of the optic canal.
The floor (inferior wall) of the bony orbit, which is also the roof of the maxillary sinus, consists primarily of the orbital surface of the maxilla (Fig. 8.76), with small contributions from the zygomatic and palatine bones.
Beginning posteriorly and continuing along the lateral boundary of the floor of the bony orbit is the inferior orbital fissure. Beyond the anterior end of the fissure the zygomatic bone completes the floor of the bony orbit.
Posteriorly, the orbital process of the palatine bone makes a small contribution to the floor of the bony orbit near the junction of the maxilla, ethmoid, and sphenoid bones.
The lateral wall of the bony orbit consists of contributions from two bones—anteriorly, the zygomatic bone and posteriorly, the greater wing of the sphenoid bone (Fig. 8.76). The superior orbital fissure is between the greater wing of the sphenoid and the lesser wing of the sphenoid that forms part of the roof.
The upper and lower eyelids are anterior structures that, when closed, protect the surface of the eyeball.
The space between the eyelids, when they are open, is the palpebral fissure.
The layers of the eyelids, from anterior to posterior, consist of skin, subcutaneous tissue, voluntary muscle, the orbital septum, the tarsus, and conjunctiva (Fig. 8.77).
The upper and lower eyelids are basically similar in structure except for the addition of two muscles in the upper eyelid.
The skin of the eyelids is not particularly substantial, and only a thin layer of connective tissue separates the skin from the underlying voluntary muscle layer (Fig. 8.77). The thin layer of connective tissue and its loose arrangement account for the accumulation of fluid (blood) when an injury occurs. |
The muscle fibers encountered next in an anteroposterior direction through the eyelid belong to the palpebral part of the orbicularis oculi (Fig. 8.77). This muscle is part of the larger orbicularis oculi muscle, which consists primarily of two parts—an orbital part, which surrounds the orbit, and the palpebral part, which is in the eyelids. The orbicularis oculi is innervated by the facial nerve [VII] and closes the eyelids.
The palpebral part is thin and anchored medially by the medial palpebral ligament (Fig. 8.78), which attaches to the anterior lacrimal crest and laterally blends with fibers from the muscle in the lower eyelid at the lateral palpebral ligament (Fig. 8.78).
A third part of the orbicularis oculi muscle that can be identified consists of fibers on the medial border, which pass deeply to attach to the posterior lacrimal crest. These fibers form the lacrimal part of the orbicularis oculi, which may be involved in the drainage of tears.
Deep to the palpebral part of the orbicularis oculi is an extension of periosteum into both the upper and lower eyelids from the margin of the orbit (Fig. 8.79). This is the orbital septum, which extends downward into the upper eyelid and upward into the lower eyelid and is continuous with the periosteum outside and inside the orbit (Fig. 8.79). The orbital septum attaches to the tendon of the levator palpebrae superioris muscle in the upper eyelid and attaches to the tarsus in the lower eyelid.
Providing major support for each eyelid is the tarsus (Fig. 8.80). There is a large superior tarsus in the upper eyelid and a smaller inferior tarsus in the lower eyelid (Fig. 8.80). These plates of dense connective tissue are attached medially to the anterior lacrimal crest of the maxilla by the medial palpebral ligament and laterally to the orbital tubercle on the zygomatic bone by the lateral palpebral ligament.
Although the tarsal plates in the upper and lower eyelids are generally similar in structure and function, there is one unique difference. Associated with the tarsus in the upper eyelid is the levator palpebrae superioris muscle (Fig. 8.80), which raises the eyelid. Its origin is from the posterior part of the roof of the orbit, just superior to the optic foramen, and it inserts into the anterior surface of the superior tarsus, with the possibility of a few fibers attaching to the skin of the upper eyelid. It is innervated by the oculomotor nerve [III].
In companion with the levator palpebrae superioris muscle is a collection of smooth muscle fibers passing from the inferior surface of the levator to the upper edge of the superior tarsus (see Fig. 8.77). Innervated by postganglionic sympathetic fibers from the superior cervical ganglion, this muscle is the superior tarsal muscle.
Loss of function of either the levator palpebrae superioris muscle or the superior tarsal muscle results in a ptosis or drooping of the upper eyelid.
The structure of the eyelid is completed by a thin membrane (the conjunctiva), which covers the posterior surface of each eyelid (see Fig. 8.77). This membrane covers the full extent of the posterior surface of each eyelid before reflecting onto the outer surface (sclera) of the eyeball. It attaches to the eyeball at the junction between the sclera and the cornea. With this membrane in place, a conjunctival sac is formed when the eyelids are closed, and the upper and lower extensions of this sac are the superior and inferior conjunctival fornices (Fig. 8.77). |
Embedded in the tarsal plates are tarsal glands (see Fig. 8.77), which empty onto the free margin of each eyelid. These glands are modified sebaceous glands and secrete an oily substance that increases the viscosity of the tears and decreases the rate of evaporation of tears from the surface of the eyeball. Blockage and inflammation of a tarsal gland is a chalazion and is on the inner surface of the eyelid.
The tarsal glands are not the only glands associated with the eyelids. Associated with the eyelash follicles are sebaceous and sweat glands (see Fig. 8.77). Blockage and inflammation of either of these is a stye and is on the edge of the eyelid.
The arterial supply to the eyelids is from the numerous vessels in the area (Fig. 8.81). They include: the supratrochlear, supra-orbital, lacrimal, and dorsal nasal arteries from the ophthalmic artery; the angular artery from the facial artery; the transverse facial artery from the superficial temporal artery; and branches from the superficial temporal artery itself.
Venous drainage follows an external pattern through veins associated with the various arteries and an internal pattern moving into the orbit through connections with the ophthalmic veins.
Lymphatic drainage is primarily to the parotid nodes, with some drainage from the medial corner of the eye along lymphatic vessels associated with the angular and facial arteries to the submandibular nodes.
Innervation of the eyelids includes both sensory and motor components.
The sensory nerves are all branches of the trigeminal nerve [V] (Fig. 8.82). Palpebral branches arise from: the supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve [V1]; and the infra-orbital branch of the maxillary nerve [V2].
Motor innervation is from: the facial nerve [VII], which innervates the palpebral part of the orbicularis oculi; the oculomotor nerve [III], which innervates the levator palpebrae superioris; and sympathetic fibers, which innervate the superior tarsal muscle.
Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly and the lower eyelid droops away, resulting in a spillage of tears.
Loss of innervation of the levator palpebrae superioris by the oculomotor nerve causes an inability to open the superior eyelid voluntarily, producing a complete ptosis.
Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis.
The lacrimal apparatus is involved in the production, movement, and drainage of fluid from the surface of the eyeball. It is made up of the lacrimal gland and its ducts, the lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct.
The lacrimal gland is anterior in the superolateral region of the orbit (Fig. 8.83) and is divided into two parts by the levator palpebrae superioris (Fig. 8.84):
The larger orbital part is in a depression, the lacrimal fossa, in the frontal bone.
The smaller palpebral part is inferior to the levator palpebrae superioris in the superolateral part of the eyelid.
Numerous ducts empty the glandular secretions into the lateral part of the superior fornix of the conjunctiva.
Fluid is continually being secreted by the lacrimal gland and moved across the surface of the eyeball from lateral to medial as the eyelids blink. |
The fluid accumulates medially in the lacrimal lake and is drained from the lake by the lacrimal canaliculi, one canaliculus associated with each eyelid (Fig. 8.83). The lacrimal punctum is the opening through which fluid enters each canaliculus.
Passing medially, the lacrimal canaliculi eventually join the lacrimal sac between the anterior and posterior lacrimal crests, posterior to the medial palpebral ligament and anterior to the lacrimal part of the orbicularis oculi muscle (Figs. 8.85 and 8.86). When the orbicularis oculi muscle contracts during blinking, the small lacrimal part of the muscle may dilate the lacrimal sac and draw tears into it through the canaliculi from the conjunctival sac.
The innervation of the lacrimal gland involves three different components (Fig. 8.87).
Sensory neurons from the lacrimal gland return to the CNS through the lacrimal branch of the ophthalmic nerve [V1].
Secretomotor fibers from the parasympathetic part of the autonomic division of the PNS stimulate fluid secretion from the lacrimal gland. These preganglionic parasympathetic neurons leave the CNS in the facial nerve [VII], enter the greater petrosal nerve (a branch of the facial nerve [VII]), and continue with this nerve until it becomes the nerve of the pterygoid canal (Fig. 8.87).
The nerve of the pterygoid canal eventually joins the pterygopalatine ganglion where the preganglionic parasympathetic neurons synapse on postganglionic parasympathetic neurons. The postganglionic neurons join the maxillary nerve [V2] and continue with it until the zygomatic nerve branches from it, and travel with the zygomatic nerve until it gives off the zygomaticotemporal nerve, which eventually distributes postganglionic parasympathetic fibers in a small branch that joins the lacrimal nerve. The lacrimal nerve passes to the lacrimal gland.
Sympathetic innervation of the lacrimal gland follows a similar path as parasympathetic innervation. Postganglionic sympathetic fibers originating in the superior cervical ganglion travel along the plexus surrounding the internal carotid artery (Fig. 8.87). They leave this plexus as the deep petrosal nerve and join the parasympathetic fibers in the nerve of the pterygoid canal. Passing through the pterygopalatine ganglion, the sympathetic fibers from this point onward follow the same path as the parasympathetic fibers to the lacrimal gland.
The arterial supply to the lacrimal gland is by branches from the ophthalmic artery and venous drainage is through the ophthalmic veins.
Numerous structures enter and leave the orbit through a variety of openings (Fig. 8.88).
When the bony orbit is viewed from an anterolateral position, the round opening at the apex of the pyramidal-shaped orbit is the optic canal, which opens into the middle cranial fossa and is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid. Passing through the optic canal are the optic nerve and the ophthalmic artery (Fig. 8.89).
Just lateral to the optic canal is a triangular-shaped gap between the roof and lateral wall of the bony orbit. This is the superior orbital fissure and allows structures to pass between the orbit and the middle cranial fossa (Fig. 8.88).
Passing through the superior orbital fissure are the superior and inferior branches of the oculomotor nerve [III], the trochlear nerve [IV], the abducent nerve [VI], the lacrimal, frontal, and nasociliary branches of the ophthalmic nerve [V1], and the superior ophthalmic vein (Fig. 8.89). |
Separating the lateral wall of the orbit from the floor of the orbit is a longitudinal opening, the inferior orbital fissure (Fig. 8.88). Its borders are the greater wing of the sphenoid and the maxilla, palatine, and zygomatic bones. This long fissure allows communication between: the orbit and the pterygopalatine fossa posteriorly, the orbit and the infratemporal fossa in the middle, and the orbit and the temporal fossa posterolaterally.
Passing through the inferior orbital fissure are the maxillary nerve [V2] and its zygomatic branch, the infra-orbital vessels, and a vein communicating with the pterygoid plexus of veins.
Beginning posteriorly and crossing about two-thirds of the inferior orbital fissure, a groove (the infra-orbital groove) is encountered, which continues anteriorly across the floor of the orbit (Fig. 8.88). This groove connects with the infra-orbital canal that opens onto the face at the infra-orbital foramen.
The infra-orbital nerve, part of the maxillary nerve [V2], and vessels pass through this structure as they exit onto the face.
Associated with the medial wall of the bony orbit are several smaller openings (Fig. 8.88).
The anterior and posterior ethmoidal foramina are at the junction between the superior and medial walls. These openings provide exits from the orbit into the ethmoid bone for the anterior and posterior ethmoidal nerves and vessels.
Completing the openings on the medial wall is a canal in the lower part of the wall anteriorly. Clearly visible is the depression for the lacrimal sac formed by the lacrimal bone and the frontal process of the maxilla. This depression is continuous with the nasolacrimal canal, which leads to the inferior nasal meatus. Contained within the nasolacrimal canal is the nasolacrimal duct, a part of the lacrimal apparatus.
The periosteum lining the bones that form the orbit is the periorbita (Fig. 8.90A). It is continuous at the margins of the orbit with the periosteum on the outer surface of the skull and sends extensions into the upper and lower eyelids (the orbital septa).
At the various openings where the orbit communicates with the cranial cavity the periorbita is continuous with the periosteal layer of dura mater. In the posterior part of the orbit, the periorbita thickens around the optic canal and the central part of the superior orbital fissure. This is the point of origin of the four rectus muscles and is the common tendinous ring.
Fascial sheath of the eyeball
The fascial sheath of the eyeball (bulbar sheath) is a layer of fascia that encloses a major part of the eyeball (Figs. 8.91 and 8.92):
Posteriorly, it is firmly attached to the sclera (the white part of the eyeball) around the point of entrance of the optic nerve into the eyeball.
Anteriorly, it is firmly attached to the sclera near the edge of the cornea (the clear part of the eyeball).
Additionally, as the muscles approach the eyeball, the investing fascia surrounding each muscle blends with the fascial sheath of the eyeball as the muscles pass through and continue to their point of attachment.
A specialized lower part of the fascial sheath of the eyeball is the suspensory ligament (Figs. 8.91 and 8.92), which supports the eyeball. This “sling-like” structure is made up of the fascial sheath of the eyeball and contributions from the two inferior ocular muscles and the medial and lateral ocular muscles.
Check ligaments of the medial and lateral
Other fascial specializations in the orbit are the check ligaments (Fig. 8.92). These are expansions of the investing fascia covering the medial and lateral rectus muscles, which attach to the medial and lateral walls of the bony orbit: |
The medial check ligament is an extension from the fascia covering the medial rectus muscle and attaches immediately posterior to the posterior lacrimal crest of the lacrimal bone.
The lateral check ligament is an extension from the fascia covering the lateral rectus muscle and is attached to the orbital tubercle of the zygomatic bone.
Functionally, the positioning of these ligaments seems to restrict the medial and lateral rectus muscles, thus the names of the fascial specializations.
There are two groups of muscles within the orbit: extrinsic muscles of eyeball (extra-ocular muscles) involved in movements of the eyeball or raising upper eyelids, and intrinsic muscles within the eyeball, which control the shape of the lens and size of the pupil.
The extrinsic muscles include the levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique.
The intrinsic muscles include the ciliary muscle, the sphincter pupillae, and the dilator pupillae.
Of the seven muscles in the extrinsic group of muscles, one raises the eyelids, whereas the other six move the eyeball itself (Table 8.8).
The movements of the eyeball, in three dimensions, (Fig. 8.93) are: elevation—moving the pupil superiorly, depression—moving the pupil inferiorly, abduction—moving the pupil laterally, adduction—moving the pupil medially, internal rotation (intorsion)—rotating the upper part of the pupil medially (or toward the nose), and external rotation (extorsion)—rotating the upper part of the pupil laterally (or toward the temple).
The axis of each orbit is directed slightly laterally from back to front, but each eyeball is directed anteriorly (Fig. 8.94). Therefore the pull of some muscles has multiple effects on the movement of the eyeball, whereas that of others has a single effect.
Levator palpebrae superioris raises the upper eyelid (Table 8.8). It is the most superior muscle in the orbit, originating from the roof, just anterior to the optic canal on the inferior surface of the lesser wing of the sphenoid (Fig. 8.95B). Its primary point of insertion is into the anterior surface of the superior tarsus, but a few fibers also attach to the skin of the upper eyelid and the superior conjunctival fornix.
Innervation is by the superior branch of the oculomotor nerve [III].
Contraction of the levator palpebrae superioris raises the upper eyelid.
A unique feature of the levator palpebrae superioris is that a collection of smooth muscle fibers passes from its inferior surface to the upper edge of the superior tarsus (see Fig. 8.77). This group of smooth muscle fibers (the superior tarsal muscle) help maintain eyelid elevation and are innervated by postganglionic sympathetic fibers from the superior cervical ganglion.
Loss of oculomotor nerve [III] function results in complete ptosis or drooping of the superior eyelid, whereas loss of sympathetic innervation to the superior tarsal muscle results in partial ptosis.
Four rectus muscles occupy medial, lateral, inferior, and superior positions as they pass from their origins posteriorly to their points of attachment on the anterior half of the eyeball (Fig. 8.95 and Table 8.8). They originate as a group from a common tendinous ring at the apex of the orbit and form a cone of muscles as they pass forward to their attachment on the eyeball.
The superior and inferior rectus muscles have complicated actions because the apex of the orbit, where the muscles originate, is medial to the central axis of the eyeball when looking directly forward:
The superior rectus originates from the superior part of the common tendinous ring above the optic canal.
The inferior rectus originates from the inferior part of the common tendinous ring below the optic canal (Fig. 8.96). |
As these muscles pass forward in the orbit to attach to the anterior half of the eyeball, they are also directed laterally (Fig. 8.95). Because of these orientations:
Contraction of the superior rectus elevates, adducts, and internally rotates the eyeball (Fig. 8.97A).
Contraction of the inferior rectus depresses, adducts, and externally rotates the eyeball (Fig. 8.97A).
The superior branch of the oculomotor nerve [III] innervates the superior rectus, and the inferior branch of the oculomotor nerve [III] innervates the inferior rectus.
To isolate the function of and to test the superior and inferior rectus muscles, a patient is asked to track a physician’s finger laterally and then either upward or downward (Fig. 8.97B). The first movement brings the axis of the eyeball into alignment with the long axis of the superior and inferior rectus muscles. Moving the finger upward tests the superior rectus muscle and moving it downward tests the inferior rectus muscle (Fig. 8.97B).
The orientation and actions of the medial and lateral rectus muscles are more straightforward than those of the superior and inferior rectus muscles.
The medial rectus originates from the medial part of the common tendinous ring medial to and below the optic canal, whereas the lateral rectus originates from the lateral part of the common tendinous ring as the common tendinous ring bridges the superior orbital fissure (Fig. 8.96).
The medial and lateral rectus muscles pass forward and attach to the anterior half of the eyeball (Fig. 8.95). Contraction of medial rectus adducts the eyeball, whereas contraction of lateral rectus abducts the eyeball (Fig. 8.97A).
The inferior branch of the oculomotor nerve [III] innervates the medial rectus, and the abducent nerve [VI] innervates the lateral rectus.
To isolate the function of and test the medial and lateral rectus muscles, a patient is asked to track a physician’s finger medially and laterally, respectively, in the horizontal plane (Fig. 8.97B).
The oblique muscles are in the superior and inferior parts of the orbit, do not originate from the common tendinous ring, are angular in their approaches to the eyeball, and, unlike the rectus muscles, attach to the posterior half of the eyeball (Table 8.8).
The superior oblique arises from the body of the sphenoid, superior and medial to the optic canal and medial to the origin of the levator palpebrae superioris (Figs. 8.95 and 8.96). It passes forward, along the medial border of the roof of the orbit, until it reaches a fibrocartilaginous pulley (the trochlea), which is attached to the trochlear fovea of the frontal bone.
The tendon of the superior oblique passes through the trochlea and turns laterally to cross the eyeball in a posterolateral direction. It continues deep to the superior rectus muscle and inserts into the outer posterior quadrant of the eyeball.
Contraction of the superior oblique therefore directs the pupil down and out (Fig. 8.97A).
The trochlear nerve [IV] innervates the superior oblique along its superior surface.
To isolate the function of and to test the superior oblique muscle, a patient is asked to track a physician’s finger medially to bring the axis of the tendon of the muscle into alignment with the axis of the eyeball, and then to look down, which tests the muscle (Fig. 8.97B).
The inferior oblique is the only extrinsic muscle that does not take origin from the posterior part of the orbit. It arises from the medial side of the floor of the orbit, just posterior to the orbital rim, and is attached to the orbital surface of the maxilla just lateral to the nasolacrimal groove (Fig. 8.95). |
The inferior oblique crosses the floor of the orbit in a posterolateral direction between the inferior rectus and the floor of the orbit, before inserting into the outer posterior quadrant just under the lateral rectus.
Contraction of the inferior oblique directs the pupil up and out (Fig. 8.97A).
The inferior branch of the oculomotor nerve innervates the inferior oblique.
To isolate the function of and to test the inferior oblique muscle, a patient is asked to track a physician’s finger medially to bring the axis of the eyeball into alignment with the axis of the muscle and then to look up, which tests the muscle (Fig. 8.97B).
Six of the seven extrinsic muscles of the orbit are directly involved in movements of the eyeball.
For each of the rectus muscles, the medial, lateral, inferior, and superior, and the superior and inferior obliques, a specific action or group of actions can be described (Table 8.8). However, these muscles do not act in isolation. They work as teams of muscles in the coordinated movement of the eyeball to position the pupil as needed.
For example, although the lateral rectus is the muscle primarily responsible for moving the eyeball laterally, it is assisted in this action by the superior and inferior oblique muscles.
The arterial supply to the structures in the orbit, including the eyeball, is by the ophthalmic artery (Fig. 8.99). This vessel is a branch of the internal carotid artery, given off immediately after the internal carotid artery leaves the cavernous sinus. The ophthalmic artery passes into the orbit through the optic canal with the optic nerve.
In the orbit the ophthalmic artery initially lies inferior and lateral to the optic nerve (Fig. 8.99). As it passes forward in the orbit, it crosses superior to the optic nerve and proceeds anteriorly on the medial side of the orbit. |
In the orbit the ophthalmic artery gives off numerous branches as follows: the lacrimal artery, which arises from the ophthalmic artery on the lateral side of the optic nerve, and passes anteriorly on the lateral side of the orbit, supplying the lacrimal gland, muscles, the anterior ciliary branch to the eyeball, and the lateral sides of the eyelid; the central retinal artery, which enters the optic nerve, proceeds down the center of the nerve to the retina, and is clearly seen when viewing the retina with an ophthalmoscope—occlusion of this vessel or of the parent artery leads to blindness; the long and short posterior ciliary arteries, which are branches that enter the eyeball posteriorly, piercing the sclera, and supplying structures inside the eyeball; the muscular arteries, which are branches supplying the intrinsic muscles of the eyeball; the supra-orbital artery, which usually arises from the ophthalmic artery immediately after it has crossed the optic nerve, proceeds anteriorly, and exits the orbit through the supra-orbital foramen with the supra-orbital nerve—it supplies the forehead and scalp as it passes across these areas to the vertex of the skull; the posterior ethmoidal artery, which exits the orbit through the posterior ethmoidal foramen to supply the ethmoidal cells and nasal cavity; the anterior ethmoidal artery, which exits the orbit through the anterior ethmoidal foramen, enters the cranial cavity giving off the anterior meningeal branch, and continues into the nasal cavity supplying the septum and lateral wall, and ending as the dorsal nasal artery; the medial palpebral arteries, which are small branches supplying the medial area of the upper and lower eyelids; the dorsal nasal artery, which is one of the two terminal branches of the ophthalmic artery, leaves the orbit to supply the upper surface of the nose; and the supratrochlear artery, which is the other terminal branch of the ophthalmic artery and leaves the orbit with the supratrochlear nerve, supplying the forehead as it passes across it in a superior direction.
There are two venous channels in the orbit, the superior and inferior ophthalmic veins (Fig. 8.100).
The superior ophthalmic vein begins in the anterior area of the orbit as connecting veins from the supra-orbital vein and the angular vein join together. It passes across the superior part of the orbit, receiving tributaries from the companion veins to the branches of the ophthalmic artery and veins draining the posterior part of the eyeball. Posteriorly, it leaves the orbit through the superior orbital fissure and enters the cavernous sinus.
The inferior ophthalmic vein is smaller than the superior ophthalmic vein, begins anteriorly, and passes across the inferior part of the orbit. It receives various tributaries from muscles and the posterior part of the eyeball as it crosses the orbit.
The inferior ophthalmic vein leaves the orbit posteriorly by: joining with the superior ophthalmic vein, passing through the superior orbital fissure on its own to join the cavernous sinus, or passing through the inferior orbital fissure to join with the pterygoid plexus of veins in the infratemporal fossa.
Because the ophthalmic veins communicate with the cavernous sinus, they act as a route by which infections can spread from outside to inside the cranial cavity.
Numerous nerves pass into the orbit and innervate structures within its bony walls. They include the optic nerve [II], the oculomotor nerve [III], the trochlear nerve [IV], the abducent nerve [VI], and autonomic nerves. Other nerves such as the ophthalmic nerve [V1] innervate orbital structures and then travel out of the orbit to innervate other regions. |
The optic nerve [II] is not a true cranial nerve, but rather an extension of the brain carrying afferent fibers from the retina of the eyeball to the visual centers of the brain. The optic nerve is surrounded by the cranial meninges, including the subarachnoid space, which extends as far forward as the eyeball.
Any increase in intracranial pressure therefore results in increased pressure in the subarachnoid space surrounding the optic nerve. This may impede venous return along the retinal veins, causing edema of the optic disc (papilledema), which can be seen when the retina is examined using an ophthalmoscope.
The optic nerve leaves the orbit through the optic canal (Fig. 8.101). It is accompanied in the optic canal by the ophthalmic artery.
The oculomotor nerve [III] leaves the anterior surface of the brainstem between the midbrain and the pons. It passes forward in the lateral wall of the cavernous sinus.
Just before entering the orbit the oculomotor nerve [III] divides into superior and inferior branches (Fig.
8.102). These branches enter the orbit through the superior orbital fissure, lying within the common tendinous ring (Fig. 8.101).
Inside the orbit the small superior branch passes upward over the lateral side of the optic nerve to innervate the superior rectus and levator palpebrae superioris muscles (Fig. 8.102).
The large inferior branch divides into three branches: one passing below the optic nerve as it passes to the medial side of the orbit to innervate the medial rectus muscle, a second descending to innervate the inferior rectus muscle, and the third descending as it runs forward along the floor of the orbit to innervate the inferior oblique muscle (Fig. 8.102).
As the third branch descends, it gives off the branch to the ciliary ganglion. This is the parasympathetic root to the ciliary ganglion and carries preganglionic parasympathetic fibers that will synapse in the ciliary ganglion with postganglionic parasympathetic fibers. The postganglionic fibers are distributed to the eyeball through short ciliary nerves and innervate the sphincter pupillae and ciliary muscles.
The trochlear nerve [IV] arises from the posterior surface of the midbrain, and passes around the midbrain to enter the edge of the tentorium cerebelli. It continues on an intradural path arriving in and passing through the lateral wall of the cavernous sinus just below the oculomotor nerve [III].
Just before entering the orbit, the trochlear nerve ascends, passing across the oculomotor nerve [III] and entering the orbit through the superior orbital fissure above the common tendinous ring (Fig. 8.101). In the orbit the trochlear nerve [IV] ascends and turns medially, crossing above the levator palpebrae superioris muscle to enter the upper border of the superior oblique muscle (Fig. 8.103).
The abducent nerve [VI] arises from the brainstem between the pons and medulla. It enters the dura covering the clivus and continues in a dural canal until it reaches the cavernous sinus.
The abducent nerve enters the cavernous sinus and runs through the sinus lateral to the internal carotid artery. It passes out of the sinus and enters the orbit through the superior orbital fissure within the common tendinous ring (Fig. 8.101). Once in the orbit it courses laterally to supply the lateral rectus muscle.
Preganglionic sympathetic fibers arise from the upper segments of the thoracic spinal cord, mainly T1. They enter the sympathetic chain through white rami communicantes, and ascend to the superior cervical ganglion where they synapse with postganglionic sympathetic fibers.
The postganglionic fibers are distributed along the internal carotid artery and its branches. |
The postganglionic sympathetic fibers destined for the orbit travel with the ophthalmic artery. Once in the orbit the fibers are distributed to the eyeball either by: passing through the ciliary ganglion, without synapsing, and joining the short ciliary nerves, which pass from the ganglion to the eyeball; or passing through long ciliary nerves to reach the eyeball.
In the eyeball postganglionic sympathetic fibers innervate the dilator pupillae muscle.
The ophthalmic nerve [V1] is the smallest and most superior of the three divisions of the trigeminal nerve. This purely sensory nerve receives input from structures in the orbit and from additional branches on the face and scalp.
Leaving the trigeminal ganglion, the ophthalmic nerve [V1] passes forward in the lateral wall of the cavernous sinus inferior to the trochlear [IV] and oculomotor [III] nerves. Just before it enters the orbit it divides into three branches—the nasociliary, lacrimal, and frontal nerves (Fig. 8.104). These branches enter the orbit through the superior orbital fissure with the frontal and lacrimal nerves outside the common tendinous ring, and the nasociliary nerve within the common tendinous ring (Fig. 8.101).
The lacrimal nerve is the smallest of the three branches of the ophthalmic nerve [V1]. Once in the orbit it passes forward along the upper border of the lateral rectus muscle (Fig. 8.105). It receives a branch from the zygomaticotemporal nerve, which carries parasympathetic and sympathetic postganglionic fibers for distribution to the lacrimal gland.
Reaching the anterolateral aspect of the orbit, the lacrimal nerve supplies the lacrimal gland, conjunctiva, and lateral part of the upper eyelid.
The frontal nerve is the largest branch of the ophthalmic nerve [V1] and receives sensory input from areas outside the orbit. Exiting the superior orbital fissure, this branch passes forward between the levator palpebrae superioris and the periorbita on the roof of the orbit (Fig. 8.101). About midway across the orbit it divides into its two terminal branches—the supra-orbital and supratrochlear nerves (Figs. 8.104 and 8.105):
The supratrochlear nerve continues forward in an anteromedial direction, passing above the trochlea, exits the orbit medial to the supra-orbital foramen, and supplies the conjunctiva and skin of the upper eyelid and the skin on the lower medial part of the forehead.
The supra-orbital nerve is the larger of the two branches, continues forward, passing between the levator palpebrae superioris muscle and the periorbita covering the roof of the orbit (Fig. 8.105), exits the orbit through the supra-orbital notch and ascends across the forehead and scalp, supplying the upper eyelid and conjunctiva, the forehead, and as far posteriorly as the middle of the scalp.
The nasociliary nerve is intermediate in size between the frontal and lacrimal nerves and is usually the first branch from the ophthalmic nerve (Fig. 8.104). It is most deeply placed in the orbit, entering the area within the common tendinous ring between the superior and inferior branches of the oculomotor nerve [III] (see Fig. 8.101).
Once in the orbit, the nasociliary nerve crosses the superior surface of the optic nerve as it passes in a medial direction below the superior rectus muscle (Figs. 8.104 and 8.106). Its first branch, the communicating branch with the ciliary ganglion (sensory root to the ciliary ganglion), is given off early in its path through the orbit. |
The nasociliary nerve continues forward along the medial wall of the orbit, between the superior oblique and the medial rectus muscles, giving off several branches (Fig. 8.106). These include: the long ciliary nerves, which are sensory to the eyeball but may also contain sympathetic fibers for pupillary dilation; the posterior ethmoidal nerve, which exits the orbit through the posterior ethmoidal foramen to supply posterior ethmoidal cells and the sphenoidal sinus; the infratrochlear nerve, which distributes to the medial part of the upper and lower eyelids, the lacrimal sac, and skin of the upper half of the nose; and the anterior ethmoidal nerve, which exits the orbit through the anterior ethmoidal foramen to supply the anterior cranial fossa, nasal cavity, and skin of the lower half of the nose (Fig. 8.106).
The ciliary ganglion is a parasympathetic ganglion of the oculomotor nerve [III]. It is associated with the nasociliary branch of the ophthalmic nerve [V1] and is the site where preganglionic and postganglionic parasympathetic neurons synapse as fibers from this part of the autonomic division of the PNS make their way to the eyeball. The ciliary ganglion is also traversed by postganglionic sympathetic fibers and sensory fibers as they travel to the eyeball.
The ciliary ganglion is a very small ganglion, in the posterior part of the orbit immediately lateral to the optic nerve and between the optic nerve and the lateral rectus muscle (Fig. 8.106). It is usually described as receiving at least two, and possibly three, branches or roots from other nerves in the orbit.
As the inferior branch of the oculomotor nerve [III] passes the area of the ciliary ganglion, it sends a branch to the ganglion (the parasympathetic root). The parasympathetic branch carries preganglionic parasympathetic fibers, which enter the ganglion and synapse with postganglionic parasympathetic fibers within the ganglion (Fig. 8.107).
The postganglionic parasympathetic fibers leave the ganglion through short ciliary nerves, which enter the posterior aspect of the eyeball around the optic nerve.
In the eyeball the parasympathetic fibers innervate: the sphincter pupillae muscle, responsible for pupillary constriction, and the ciliary muscle, responsible for accommodation of the lens of the eye for near vision.
A second branch (the sensory root), passes from the nasociliary nerve to the ganglion (Fig. 8.107). This branch enters the posterosuperior aspect of the ganglion, and carries sensory fibers, which pass through the ganglion and continue along the short ciliary nerves to the eyeball. These fibers are responsible for sensory innervation to all parts of the eyeball; however, the sympathetic fibers also may take alternative routes to the eyeball.
The third branch to the ciliary ganglion is the most variable. This branch, when present, is the sympathetic root and contains postganglionic sympathetic fibers from the superior cervical ganglion (Fig. 8.107). These fibers travel up the internal carotid artery, leave the plexus surrounding the artery in the cavernous sinus, and enter the orbit through the common tendinous ring. In the orbit they enter the posterior aspect of the ciliary ganglion, cross the ganglion, and continue along the short ciliary nerves to the eyeball; however, the sympathetic fibers also may take alternative routes to the eyeball. |
Sympathetic fibers to the eyeball may not enter the ganglion as a separate sympathetic root. Rather, the postganglionic sympathetic fibers may leave the plexus associated with the internal carotid artery in the cavernous sinus, join the ophthalmic nerve [V1], and course into the ciliary ganglion in the sensory root from the nasociliary nerve. In addition, the sympathetic fibers carried in the nasociliary nerve may not enter the ganglion at all and may course directly into the eyeball in the long ciliary nerves (Fig. 8.107). Whatever their path, postganglionic sympathetic fibers reach the eyeball and innervate the dilator pupillae muscle.
The globe-shaped eyeball occupies the anterior part of the orbit. Its rounded shape is disrupted anteriorly, where it bulges outward. This outward projection represents about one-sixth of the total area of the eyeball and is the transparent cornea (Fig. 8.108).
Posterior to the cornea and in order from front to back are the anterior chamber, the iris and pupil, the posterior chamber, the lens, the postremal (vitreous) chamber, and the retina.
The anterior chamber is the area directly posterior to the cornea and anterior to the colored part of the eye (iris). The central opening in the iris is the pupil. Posterior to the iris and anterior to the lens is the smaller posterior chamber.
The anterior and posterior chambers are continuous with each other through the pupillary opening. They are filled with a fluid (aqueous humor), which is secreted into the posterior chamber, flows into the anterior chamber through the pupil, and is absorbed into the scleral venous sinus (the canal of Schlemm), which is a circular venous channel at the junction between the cornea and the iris (Fig. 8.108).
The aqueous humor supplies nutrients to the avascular cornea and lens and maintains the intra-ocular pressure. If the normal cycle of its production and absorption is disturbed so that the amount of fluid increases, intra-ocular pressure will increase. This condition (glaucoma) can lead to a variety of visual problems.
The lens separates the anterior one-fifth of the eyeball from the posterior four-fifths (Fig. 8.108). It is a transparent, biconvex elastic disc attached circumferentially to muscles associated with the outer wall of the eyeball. This lateral attachment provides the lens with the ability to change its refractive ability to maintain visual acuity. The clinical term for opacity of the lens is a cataract.
The posterior four-fifths of the eyeball, from the lens to the retina, is occupied by the postremal (vitreous) chamber (Fig. 8.108). This segment is filled with a transparent, gelatinous substance—the vitreous body (vitreous humor). This substance, unlike aqueous humor, cannot be replaced.
Walls of the eyeball
Surrounding the internal components of the eyeball are the walls of the eyeball. They consist of three layers: an outer fibrous layer, a middle vascular layer, and an inner retinal layer (Fig. 8.108).
The outer fibrous layer consists of the sclera posteriorly and the cornea anteriorly.
The middle vascular layer consists of the choroid posteriorly and is continuous with the ciliary body and iris anteriorly.
The inner layer consists of the optic part of the retina posteriorly and the nonvisual retina that covers the internal surface of the ciliary body and iris anteriorly.
The arterial supply to the eyeball is from several sources:
The short posterior ciliary arteries are branches from the ophthalmic artery that pierce the sclera around the optic nerve and enter the choroid layer (Fig. 8.108).
The long posterior ciliary arteries, usually two, enter the sclera on the medial and lateral sides of the optic nerve and proceed anteriorly in the choroid layer to anastomose with the anterior ciliary arteries. |
The anterior ciliary arteries are branches of the arteries supplying the muscles (Fig. 8.108)—as the muscles attach to the sclera, these arteries pierce the sclera to anastomose with the long posterior ciliary arteries in the choroid layer.
The central retinal artery that has traversed the optic nerve and enters the area of the retina at the optic disc.
Venous drainage of the eyeball is primarily related to drainage of the choroid layer. Four large veins (the vorticose veins) are involved in this process. They exit through the sclera from each of the posterior quadrants of the eyeball and enter the superior and inferior ophthalmic veins. There is also a central retinal vein accompanying the central retinal artery.
Fibrous layer of the eyeball
The fibrous layer of the eyeball consists of two components—the sclera covers the posterior and lateral parts of the eyeball, about five-sixths of the surface, and the cornea covers the anterior part (Fig. 8.108).
The sclera is an opaque layer of dense connective tissue that can be seen anteriorly through its conjunctival covering as the “white of the eye.” It is pierced by numerous vessels and nerves, including the optic nerve posteriorly and provides attachment for the various muscles involved in eyeball movements.
The fascial sheath of the eyeball covers the surface of the sclera externally from the entrance of the optic nerve to the corneoscleral junction while internally the surface of the sclera is loosely attached to the choroid of the vascular layer.
Continuous with the sclera anteriorly is the transparent cornea. It covers the anterior one-sixth of the surface of the eyeball and, being transparent, allows light to enter the eyeball.
Vascular layer of the eyeball
The vascular layer of the eyeball consists of three continuous parts—the choroid, the ciliary body, and the iris from posterior to anterior (Fig. 8.108).
The choroid is posterior and represents approximately two-thirds of the vascular layer. It is a thin, highly vascular, pigmented layer consisting of smaller vessels adjacent to the retina and larger vessels more peripherally. It is firmly attached to the retina internally and loosely attached to the sclera externally.
Extending from the anterior border of the choroid is the ciliary body (Fig. 8.108). This triangular-shaped structure, between the choroid and the iris, forms a complete ring around the eyeball. Its components include the ciliary muscle and the ciliary processes (Fig. 8.110).
The ciliary muscle consists of smooth muscle fibers arranged longitudinally, circularly, and radially. Controlled by parasympathetics traveling to the orbit in the oculomotor nerve [III], these muscle fibers, on contraction, decrease the size of the ring formed by the ciliary body.
The ciliary processes are longitudinal ridges projecting from the inner surface of the ciliary body (Fig. 8.110). Extending from them are zonular fibers attached to the lens of the eyeball, which suspend the lens in its proper position and collectively form the suspensory ligament of the lens.
Contraction of the ciliary muscle decreases the size of the ring formed by the ciliary body. This reduces tension on the suspensory ligament of the lens. The lens therefore becomes more rounded (relaxed) resulting in accommodation of the lens for near vision.
Ciliary processes also contribute to the formation of aqueous humor. |
Completing the vascular layer of the eyeball anteriorly is the iris (Fig. 8.108). This circular structure, projecting outward from the ciliary body, is the colored part of the eye with a central opening (the pupil). Controlling the size of the pupil are smooth muscle fibers (sphincter pupillae) and myoepithelial cells (dilator pupillae) within the iris (Fig. 8.110):
Fibers arranged in a circular pattern make up the sphincter pupillae muscle (Table 8.9), which is innervated by parasympathetics—contraction of its fibers decreases or constricts the pupillary opening.
Contractile fibers arranged in a radial pattern make up the dilator pupillae muscle, which is innervated by sympathetics—contraction of its fibers increases or dilates the pupillary opening.
Inner layer of the eyeball
The inner layer of the eyeball is the retina (Fig. 8.108). It consists of two parts. Posteriorly and laterally is the optic part of the retina, which is sensitive to light, and anteriorly is the nonvisual part, which covers the internal surface of the ciliary body and the iris. The junction between these parts is an irregular line (the ora serrata).
Optic part of the retina
The optic part of the retina consists of two layers, an outer pigmented layer and an inner neural layer:
The pigmented layer is firmly attached to the choroid and continues anteriorly over the internal surface of the ciliary body and iris.
The neural layer, which can be further subdivided into its various neural components, is only attached to the pigmented layer around the optic nerve and at the ora serrata.
It is the neural layer that separates in the case of a detached retina.
Several obvious features are visible on the posterior surface of the optic part of the retina.
The optic disc is where the optic nerve leaves the retina (Fig. 8.109). It is lighter than the surrounding retina and branches of the central retinal artery spread from this point outward to supply the retina. As there are no lightsensitive receptor cells in the optic disc, it is referred to as a blind spot in the retina.
Lateral to the optic disc a small area with a hint of yellowish coloration is the macula lutea with its central depression, the fovea centralis (Fig. 8.109). This is the thinnest area of the retina and visual sensitivity here is higher than elsewhere in the retina because it has fewer rods (light-sensitive receptor cells that function in dim light and are insensitive to color) and more cones (light-sensitive receptor cells that respond to bright light and are sensitive to color).
The ear is the organ of hearing and balance. It has three parts (Fig. 8.113):
The first part is the external ear consisting of the part attached to the lateral aspect of the head and the canal leading inward.
The second part is the middle ear—a cavity in the petrous part of the temporal bone bounded laterally, and separated from the external canal, by a membrane and connected internally to the pharynx by a narrow tube.
The third part is the internal ear consisting of a series of cavities within the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially.
The internal ear converts the mechanical signals received from the middle ear, which start as sound captured by the external ear, into electrical signals to transfer information to the brain. The internal ear also contains receptors that detect motion and position.
The external ear consists of two parts. The part projecting from the side of the head is the auricle (pinna) and the canal leading inward is the external acoustic meatus.
The auricle is on the side of the head and assists in capturing sound. It consists of cartilage covered with skin and arranged in a pattern of various elevations and depressions (Fig. 8.114).
The large outside rim of the auricle is the helix. It ends inferiorly at the fleshy lobule, the only part of the auricle not supported by cartilage. |
The hollow center of the auricle is the concha of the auricle. The external acoustic meatus leaves from the depths of this area.
Just anterior to the opening of the external acoustic meatus, in front of the concha, is an elevation (the tragus). Opposite the tragus, and above the fleshy lobule, is another elevation (the antitragus). A smaller curved rim, parallel and anterior to the helix, is the antihelix.
Numerous intrinsic and extrinsic muscles are associated with the auricle:
The intrinsic muscles pass between the cartilaginous parts of the auricle and may change the shape of the auricle.
The extrinsic muscles, the anterior, superior, and posterior auricular muscles, pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle (see Fig. 8.56).
Both groups of muscles are innervated by the facial nerve [VII].
Sensory innervation of the auricle is from many sources (Fig. 8.115):
The outer more superficial surfaces of the auricle are supplied by the great auricular nerve (anterior and posterior inferior portions) and the lesser occipital nerve (posterosuperior portion) from the cervical plexus and the auriculotemporal branch of the mandibular nerve [V3] (anterosuperior portion).
The deeper parts of the auricle are supplied by the vagus nerve [X] (the auricular branch) and the facial nerve [VII] (which sends a branch to the auricular branch of the vagus nerve [X]).
The arterial supply to the auricle is from numerous sources. The external carotid artery supplies the posterior auricular artery, the superficial temporal artery supplies anterior auricular branches, and the occipital artery supplies a branch.
Venous drainage is through vessels following the arteries.
Lymphatic drainage of the auricle passes anteriorly into parotid nodes and posteriorly into mastoid nodes, and possibly into the upper deep cervical nodes.
The external acoustic meatus extends from the deepest part of the concha to the tympanic membrane (eardrum), a distance of approximately 1 inch (2.5 cm) (Fig. 8.116). Its walls consist of cartilage and bone. The lateral one-third is formed from cartilaginous extensions from some of the auricular cartilages and the medial two-thirds is a bony tunnel in the temporal bone.
Throughout its length the external acoustic meatus is covered with skin, some of which contains hair and modified sweat glands producing cerumen (earwax). Its diameter varies, being wider laterally and narrow medially.
The external acoustic meatus does not follow a straight course. From the external opening it passes upward in an anterior direction, then turns slightly posteriorly still passing upward, and finally, turns again in an anterior direction with a slight descent. For examination purposes, observation of the external acoustic meatus and tympanic membrane can be improved by pulling the ear superiorly, posteriorly, and slightly laterally.
Sensory innervation of the external acoustic meatus is from several of the cranial nerves. The major sensory input travels through branches of the auriculotemporal nerve, a branch of the mandibular nerve [V3] (anterior and superior walls), and in the auricular branch of the vagus nerve [X] (posterior and inferior walls). A minor sensory input may also come from a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X].
The tympanic membrane separates the external acoustic meatus from the middle ear (Figs. 8.117 and 8.118). It is at an angle, sloping medially from top to bottom and posteriorly to anteriorly. Its lateral surface therefore faces inferiorly and anteriorly. It consists of a connective tissue core lined with skin on the outside and mucous membrane on the inside. |
Around the periphery of the tympanic membrane a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone. At its center, a concavity is produced by the attachment on its internal surface of the lower end of the handle of the malleus, part of the malleus bone in the middle ear. This point of attachment is the umbo of the tympanic membrane.
Anteroinferior to the umbo of the tympanic membrane a bright reflection of light, referred to as the cone of light, is usually visible when examining the tympanic membrane with an otoscope.
Superior to the umbo in an anterior direction is the attachment of the rest of the handle of the malleus (Fig. 8.118). At the most superior extent of this line of attachment a small bulge in the membrane marks the position of the lateral process of the malleus as it projects against the internal surface of the tympanic membrane. Extending away from this elevation, on the internal surface of the membrane, are the anterior and posterior malleolar folds. Superior to these folds the tympanic membrane is thin and slack (the pars flaccida), whereas the rest of the membrane is thick and taut (the pars tensa).
Innervation of the external and internal surfaces of the tympanic membrane is by several cranial nerves:
Sensory innervation of the skin on the outer surface of the tympanic membrane is primarily by the auriculotemporal nerve, a branch of the mandibular nerve [V3] with additional participation of the auricular branch of the vagus nerve [X], a small contribution by a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X], and possibly a contribution from the glossopharyngeal nerve [IX].
Sensory innervation of the mucous membrane on the inner surface of the tympanic membrane is carried entirely by the glossopharyngeal [IX] nerve.
The middle ear is an air-filled, mucous membrane–lined space in the temporal bone between the tympanic membrane laterally and the lateral wall of the internal ear medially. It is described as consisting of two parts (Fig. 8.119): the tympanic cavity immediately adjacent to the tympanic membrane, and the epitympanic recess superiorly.
The middle ear communicates with the mastoid area posteriorly and the nasopharynx (via the pharyngotympanic tube) anteriorly. Its basic function is to transmit vibrations of the tympanic membrane across the cavity of the middle ear to the internal ear. It accomplishes this through three interconnected but movable bones that bridge the space between the tympanic membrane and the internal ear. These bones are the malleus (connected to the tympanic membrane), the incus (connected to the malleus by a synovial joint), and the stapes (connected to the incus by a synovial joint, and attached to the lateral wall of the internal ear at the oval window).
The middle ear has a roof and a floor, and anterior, posterior, medial, and lateral walls (Fig. 8.120).
The tegmental wall (roof) of the middle ear consists of a thin layer of bone, which separates the middle ear from the middle cranial fossa. This layer of bone is the tegmen tympani on the anterior surface of the petrous part of the temporal bone.
The jugular wall (floor) of the middle ear consists of a thin layer of bone that separates it from the internal jugular vein. Occasionally, the floor is thickened by the presence of mastoid air cells.
Near the medial border of the floor is a small aperture, through which the tympanic branch from the glossopharyngeal nerve [IX] enters the middle ear.
The membranous (lateral) wall of the middle ear consists almost entirely of the tympanic membrane, but because the tympanic membrane does not extend superiorly into the epitympanic recess, the upper part of the membranous wall of the middle ear is the bony lateral wall of the epitympanic recess. |
The mastoid (posterior) wall of the middle ear is only partially complete. The lower part of this wall consists of a bony partition between the tympanic cavity and mastoid air cells. Superiorly, the epitympanic recess is continuous with the aditus to the mastoid antrum (Figs. 8.120 and 8.121).
Associated with the mastoid wall are: the pyramidal eminence, a small elevation through which the tendon of the stapedius muscle enters the middle ear; and the opening through which the chorda tympani nerve, a branch of the facial nerve [VII], enters the middle ear.
The anterior wall of the middle ear is only partially complete. The lower part consists of a thin layer of bone that separates the tympanic cavity from the internal carotid artery. Superiorly, the wall is deficient because of the presence of: a large opening for the entrance of the pharyngotympanic tube into the middle ear, and a smaller opening for the canal containing the tensor tympani muscle.
The foramen for the exit of the chorda tympani nerve from the middle ear is also associated with this wall (Fig. 8.120).
The labyrinthine (medial) wall of the middle ear is also the lateral wall of the internal ear. A prominent structure on this wall is a rounded bulge (the promontory) produced by the basal coil of the cochlea, which is an internal ear structure involved with hearing (Fig. 8.120).
Associated with the mucous membrane covering the promontory is a plexus of nerves (the tympanic plexus), which consists primarily of contributions from the tympanic branch of the glossopharyngeal nerve [IX] and branches from the internal carotid plexus. It supplies the mucous membrane of the middle ear, the mastoid area, and the pharyngotympanic tube.
Additionally, a branch of the tympanic plexus (the lesser petrosal nerve) leaves the promontory and the middle ear, travels across the anterior surface of the petrous part of the temporal bone, and leaves the middle cranial fossa through the foramen ovale to enter the otic ganglion. Other structures associated with the labyrinthine wall are two openings, the oval and round windows, and two prominent elevations (Fig. 8.120):
The oval window is posterosuperior to the promontory, is the point of attachment for the base of the stapes (footplate), and ends the chain of bones that transfer vibrations initiated by the tympanic membrane to the cochlea of the internal ear.
The round window is posteroinferior to the promontory.
Posterior and superior to the oval window on the medial wall is the prominence of the facial canal, which is a ridge of bone produced by the facial nerve [VII] in its canal as it passes through the temporal bone.
Just above and posterior to the prominence of the facial canal is a broader ridge of bone (prominence of the lateral semicircular canal) produced by the lateral semicircular canal, which is a structure involved in detecting motion.
Posterior to the epitympanic recess of the middle ear is the aditus to the mastoid antrum, which is the opening to the mastoid antrum (Fig. 8.121).
The mastoid antrum is a cavity continuous with collections of air-filled spaces (the mastoid cells), throughout the mastoid part of the temporal bone, including the mastoid process. The mastoid antrum is separated from the middle cranial fossa above by only the thin tegmen tympani.
The mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the middle ear. Therefore infections in the middle ear can easily spread into the mastoid area. |
The pharyngotympanic tube connects the middle ear with the nasopharynx (Fig. 8.122) and equalizes pressure on both sides of the tympanic membrane. Its opening in the middle ear is on the anterior wall, and from here it extends forward, medially, and downward to enter the nasopharynx just posterior to the inferior meatus of the nasal cavity. It consists of: a bony part (the one-third nearest the middle ear); and a cartilaginous part (the remaining two-thirds).
The opening of the bony part is clearly visible on the inferior surface of the skull at the junction of the squamous and petrous parts of the temporal bone immediately posterior to the foramen ovale and foramen spinosum.
The arterial supply to the pharyngotympanic tube is from several sources. Branches arise from the ascending pharyngeal artery (a branch of the external carotid artery) and from two branches of the maxillary artery (the middle meningeal artery and the artery of the pterygoid canal).
Venous drainage of the pharyngotympanic tube is to the pterygoid plexus of veins in the infratemporal fossa.
Innervation of the mucous membrane lining the pharyngotympanic tube is primarily from the tympanic plexus because it is continuous with the mucous membrane lining the tympanic cavity, the internal surface of the tympanic membrane, and the mastoid antrum and mastoid cells. This plexus receives its major contribution from the tympanic nerve, a branch of the glossopharyngeal nerve [IX].
The bones of the middle ear consist of the malleus, incus, and stapes. They form an osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear (Fig. 8.123).
Muscles associated with the auditory ossicles modulate movement during the transmission of vibrations.
The malleus is the largest of the auditory ossicles and is attached to the tympanic membrane. Identifiable parts include the head of the malleus, neck of the malleus, anterior and lateral processes, and handle of the malleus (Fig. 8.123). The head of the malleus is the rounded upper part of the malleus in the epitympanic recess. Its posterior surface articulates with the incus.
Inferior to the head of the malleus is the constricted neck of the malleus, and below this are the anterior and lateral processes:
The anterior process is attached to the anterior wall of the middle ear by a ligament.
The lateral process is attached to the anterior and posterior malleolar folds of the tympanic membrane.
The downward extension of the malleus, below the anterior and lateral processes, is the handle of the malleus, which is attached to the tympanic membrane.
The second bone in the series of auditory ossicles is the incus. It consists of the body of the incus and long and short limbs (Fig. 8.123):
The enlarged body of the incus articulates with the head of the malleus and is in the epitympanic recess.
The long limb extends downward from the body, paralleling the handle of the malleus, and ends by bending medially to articulate with the stapes.
The short limb extends posteriorly and is attached by a ligament to the upper posterior wall of the middle ear.
The stapes is the most medial bone in the osseous chain and is attached to the oval window. It consists of the head of the stapes, anterior and posterior limbs, and the base of the stapes (Fig. 8.123):
The head of the stapes is directed laterally and articulates with the long process of the incus.
The two limbs separate from each other and attach to the oval base.
The base of the stapes fits into the oval window on the labyrinthine wall of the middle ear.
Muscles associated with the ossicles |
Two muscles are associated with the bony ossicles of the middle ear—the tensor tympani and stapedius (Fig. 8.124 and Table 8.10).
The tensor tympani muscle lies in a bony canal above the pharyngotympanic tube. It originates from the cartilaginous part of the pharyngotympanic tube, the greater wing of the sphenoid, and its own bony canal, and passes through its canal in a posterior direction, ending in a rounded tendon that inserts into the upper part of the handle of the malleus.
Innervation of the tensor tympani is by a branch from the mandibular nerve [V3].
Contraction of the tensor tympani pulls the handle of the malleus medially. This tenses the tympanic membrane, reducing the force of vibrations in response to loud noises.
The stapedius muscle is a very small muscle that originates from inside the pyramidal eminence, which is a small projection on the mastoid wall of the middle ear (Fig. 8.124). Its tendon emerges from the apex of the pyramidal eminence and passes forward to attach to the posterior surface of the neck of the stapes.
The stapedius is innervated by a branch from the facial nerve [VII].
Contraction of the stapedius muscle, usually in response to loud noises, pulls the stapes posteriorly and prevents excessive oscillation.
Numerous arteries supply the structures in the middle ear: the two largest branches are the tympanic branch of the maxillary artery and the mastoid branch of the occipital or posterior auricular arteries; smaller branches come from the middle meningeal artery, the ascending pharyngeal artery, the artery of the pterygoid canal, and tympanic branches from the internal carotid artery.
Venous drainage of the middle ear returns to the pterygoid plexus of veins and the superior petrosal sinus.
The tympanic plexus innervates the mucous membrane lining the walls and contents of the middle ear, which includes the mastoid area and the pharyngotympanic tube. It is formed by the tympanic nerve, a branch of the glossopharyngeal nerve [IX], and from branches of the internal carotid plexus. The tympanic plexus occurs in the mucous membrane covering the promontory, which is the rounded bulge on the labyrinthine wall of the middle ear (Fig. 8.125).
As the glossopharyngeal nerve [IX] exits the skull through the jugular foramen, it gives off the tympanic nerve. This branch reenters the skull through a small foramen and passes through the bone to the middle ear.
Once in the middle ear, the tympanic nerve forms the tympanic plexus, along with branches from the plexus of nerves surrounding the internal carotid artery (caroticotympanic nerves). Branches from the tympanic plexus supply the mucous membranes of the middle ear, including the pharyngotympanic tube and the mastoid area.
The tympanic plexus also gives off a major branch (the lesser petrosal nerve), which supplies preganglionic parasympathetic fibers to the otic ganglion (Fig. 8.125).
The lesser petrosal nerve leaves the area of the promontory, exits the middle ear, travels through the petrous part of the temporal bone, and exits onto the anterior surface of the petrous part of the temporal bone through a hiatus just below the hiatus for the greater petrosal nerve (Fig. 8.126). It continues diagonally across the anterior surface of the temporal bone before exiting the middle cranial fossa through the foramen ovale. Once outside the skull it enters the otic ganglion. |
The internal ear consists of a series of bony cavities (the bony labyrinth) and membranous ducts and sacs (the membranous labyrinth) within these cavities. All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially (Figs. 8.127 and 8.128).
The bony labyrinth consists of the vestibule, three semicircular canals, and the cochlea (Fig. 8.128). These bony cavities are lined with periosteum and contain a clear fluid (the perilymph).
Suspended within the perilymph but not filling all spaces of the bony labyrinth is the membranous labyrinth, which consists of the semicircular ducts, the cochlear duct, and two sacs (the utricle and the saccule). These membranous spaces are filled with endolymph.
The structures in the internal ear convey information to the brain about balance and hearing:
The cochlear duct is the organ of hearing.
The semicircular ducts, utricle, and saccule are the organs of balance.
The nerve responsible for these functions is the vestibulocochlear nerve [VIII], which divides into vestibular (balance) and cochlear (hearing) parts after entering the internal acoustic meatus (Fig. 8.128).
The vestibule, which contains the oval window in its lateral wall, is the central part of the bony labyrinth (Fig. 8.129). It communicates anteriorly with the cochlea and posterosuperiorly with the semicircular canals.
A narrow canal (the vestibular aqueduct) leaves the vestibule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone.
Projecting in a posterosuperior direction from the vestibule are the anterior, posterior, and lateral semicircular canals (Fig. 8.129). Each of these canals forms two-thirds of a circle connected at both ends to the vestibule and with one end dilated to form the ampulla. The canals are oriented so that each canal is at right angles to the other two.
Projecting in an anterior direction from the vestibule is the cochlea, which is a bony structure that twists on itself two and one-half to two and three-quarter times around a central column of bone (the modiolus). This arrangement produces a cone-shaped structure with a base of the cochlea that faces posteromedially and an apex that faces anterolaterally (Fig. 8.130). This positions the wide base of the modiolus near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibulocochlear nerve [VIII].
Extending laterally throughout the length of the modiolus is a thin lamina of bone (the lamina of the modiolus, or spiral lamina). Circling around the modiolus, and held in a central position by its attachment to the lamina of the modiolus, is the cochlear duct, which is a component of the membranous labyrinth.
Attached peripherally to the outer wall of the cochlea, the cochlear duct creates two canals (the scala vestibuli and the scala tympani), which extend throughout the cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema):
The scala vestibuli is continuous with the vestibule.
The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window (Fig. 8.131).
Finally, near the round window is a small channel (the cochlear canaliculus), which passes through the temporal bone and opens on its inferior surface into the posterior cranial fossa. This provides a connection between the perilymph-containing cochlea and the subarachnoid space (Fig. 8.131). |
The membranous labyrinth is a continuous system of ducts and sacs within the bony labyrinth. It is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph.
Consisting of two sacs (the utricle and the saccule) and four ducts (the three semicircular ducts and the cochlear duct), the membranous labyrinth has unique functions related to balance and hearing:
The utricle, saccule, and three semicircular ducts are part of the vestibular apparatus (i.e., organs of balance).
The cochlear duct is the organ of hearing.
The general organization of the parts of the membranous labyrinth (Fig. 8.131) places: the cochlear duct within the cochlea of the bony labyrinth, anteriorly, the three semicircular ducts within the three semicircular canals of the bony labyrinth, posteriorly, and the saccule and utricle within the vestibule of the bony labyrinth, in the middle.
Organs of balance
Five of the six components of the membranous labyrinth are concerned with balance. These are the two sacs (the utricle and the saccule) and three ducts (the anterior, posterior, and lateral semicircular ducts).
Utricle, saccule, and endolymphatic duct
The utricle is the larger of the two sacs. It is oval, elongated and irregular in shape and is in the posterosuperior part of the vestibule of the bony labyrinth.
The three semicircular ducts empty into the utricle. Each semicircular duct is similar in shape, including a dilated end forming the ampulla, to its complementary bony semicircular canal, only much smaller.
The saccule is a smaller, rounded sac lying in the anteroinferior part of the vestibule of the bony labyrinth (Fig. 8.131). The cochlear duct empties into it.
The utriculosaccular duct establishes continuity between all components of the membranous labyrinth and connects the utricle and saccule. Branching from this small duct is the endolymphatic duct, which enters the vestibular aqueduct (a channel through the temporal bone) to emerge onto the posterior surface of the petrous part of the temporal bone in the posterior cranial fossa. Here the endolymphatic duct expands into the endolymphatic sac, which is an extradural pouch that functions in resorption of endolymph.
Functionally, sensory receptors for balance are organized into unique structures that are located in each of the components of the vestibular apparatus. In the utricle and saccule the sense organ is the macula of the utricle and the macula of the saccule, respectively, and in the ampulla of each of the three semicircular ducts it is the crista.
The utricle responds to linear acceleration in the horizontal plane and sideways head tilts, while the saccule responds to linear acceleration in the vertical plane, such as forward-backward and upward-downward movements. In contrast, the receptors in the three semicircular ducts respond to rotational movement in any direction.
Organ of hearing
The cochlear duct has a central position in the cochlea of the bony labyrinth dividing it into two canals (the scala vestibuli and the scala tympani). It is maintained in this position by being attached centrally to the lamina of the modiolus, which is a thin lamina of bone extending from the modiolus (the central bony core of the cochlea) and peripherally to the outer wall of the cochlea (Fig. 8.132). |
Thus, the triangular-shaped cochlear duct has: an outer wall against the bony cochlea consisting of thickened, epithelial-lined periosteum (the spiral ligament), a roof (the vestibular membrane), which separates the endolymph in the cochlear duct from the perilymph in the scala vestibuli and consists of a membrane with a connective tissue core lined on either side with epithelium, and a floor, which separates the endolymph in the cochlear duct from the perilymph in the scala tympani and consists of the free edge of the lamina of the modiolus, and a membrane (the basilar membrane) extending from this free edge of the lamina of the modiolus to an extension of the spiral ligament covering the outer wall of the cochlea.
The spiral organ is the organ of hearing, rests on the basilar membrane, and projects into the enclosed, endolymph-filled cochlear duct (Fig. 8.132).
The arterial supply to the internal ear is divided between vessels supplying the bony labyrinth and the membranous labyrinth.
The bony labyrinth is supplied by the same arteries that supply the surrounding temporal bone—these include an anterior tympanic branch from the maxillary artery, a stylomastoid branch from the posterior auricular artery, and a petrosal branch from the middle meningeal artery.
The membranous labyrinth is supplied by the labyrinthine artery, which either arises from the anteroinferior cerebellar artery or is a direct branch of the basilar artery—whatever its origin, it enters the internal acoustic meatus with the facial [VII] and vestibulocochlear [VIII] nerves and eventually divides into: a cochlear branch, which passes through the modiolus and supplies the cochlear duct; and one or two vestibular branches, which supply the vestibular apparatus.
Venous drainage of the membranous labyrinth is through vestibular veins and cochlear veins, which follow the arteries. These come together to form a labyrinthine vein, which eventually empties into either the inferior petrosal sinus or the sigmoid sinus.
The vestibulocochlear nerve [VIII] carries special afferent fibers for hearing (the cochlear component) and balance (the vestibular component). It enters the lateral surface of the brainstem, between the pons and medulla, after exiting the temporal bone through the internal acoustic meatus and crossing the posterior cranial fossa.
Inside the temporal bone, at the distal end of the internal acoustic meatus, the vestibulocochlear nerve divides to form: the cochlear nerve, and the vestibular nerve.
The vestibular nerve enlarges to form the vestibular ganglion, before dividing into superior and inferior parts, which distribute to the three semicircular ducts and the utricle and saccule (see Fig. 8.128).
The cochlear nerve enters the base of the cochlea and passes upward through the modiolus. The ganglion cells of the cochlear nerve are in the spiral ganglion at the base of the lamina of the modiolus as it winds around the modiolus (Fig. 8.130). Branches of the cochlear nerve pass through the lamina of the modiolus to innervate the receptors in the spiral organ.
Facial nerve [VII] in the temporal bone
The facial nerve [VII] is closely associated with the vestibulocochlear nerve [VIII] as it enters the internal acoustic meatus of the temporal bone. Traveling through the temporal bone, its path and several of its branches are directly related to the internal and middle ears.
The facial nerve [VII] enters the internal acoustic meatus in the petrous part of the temporal bone (Fig. 8.133A). The vestibulocochlear nerve and the labyrinthine artery accompany it. |
At the distal end of the internal acoustic meatus, the facial nerve [VII] enters the facial canal and continues laterally between the internal and middle ears. At this point the facial nerve [VII] enlarges and bends posteriorly and laterally. The enlargement is the sensory geniculate ganglion. As the facial canal continues, the facial nerve [VII] turns sharply downward, and running in an almost vertical direction, it exits the skull through the stylomastoid foramen (Fig. 8.133A).
Greater petrosal nerve. At the geniculate ganglion, the facial nerve [VII] gives off the greater petrosal nerve (Fig. 8.133A). This is the first branch of the facial nerve [VII]. The greater petrosal nerve leaves the geniculate ganglion, travels anteromedially through the temporal bone, and emerges through the hiatus for the greater petrosal nerve on the anterior surface of the petrous part of the temporal bone (see Fig. 8.126). The greater petrosal nerve carries preganglionic parasympathetic fibers to the pterygopalatine ganglion.
Continuing beyond the bend, the position of the facial nerve [VII] is indicated on the medial wall of the middle ear by a bulge (see Fig. 8.125).
Nerve to stapedius and chorda tympani. Near the beginning of its vertical descent, the facial nerve [VII] gives off a small branch, the nerve to the stapedius (Fig. 8.133), which innervates the stapedius muscle, and just before it exits the skull the facial nerve [VII] gives off the chorda tympani nerve.
The chorda tympani does not immediately exit the temporal bone, but ascends to enter the middle ear through its posterior wall, passing near the upper aspect of the tympanic membrane between the malleus and incus (Fig. 8.133B). It then exits the middle ear through a canal leading to the petrotympanic fissure and exits the skull through this fissure to join the lingual nerve in the infratemporal fossa.
Transmission of sound
A sound wave enters the external acoustic meatus and strikes the tympanic membrane moving it medially (Fig. 8.134). As the handle of the malleus is attached to this membrane, it also moves medially. This moves the head of the malleus laterally. Because the heads of the malleus and incus articulate with each other, the head of the incus is also moved laterally. This pushes the long process of the incus medially. The long process articulates with the stapes, so its movement causes the stapes to move medially. In turn, because the base of the stapes is attached to the oval window, the oval window is also moved medially.
This action completes the transfer of a large-amplitude, low-force, airborne wave that vibrates the tympanic membrane into a small-amplitude, high-force vibration of the oval window, which generates a wave in the fluid-filled scala vestibuli of the cochlea.
The wave established in the perilymph of the scala vestibuli moves through the cochlea and causes an outward bulging of the secondary tympanic membrane covering the round window at the lower end of the scala tympani (Fig. 8.134). This causes the basilar membrane to vibrate, which in turn leads to stimulation of receptor cells in the spiral organ.
The receptor cells send impulses back to the brain through the cochlear part of the vestibulocochlear nerve [VIII] where they are interpreted as sound.
If the sounds are too loud, causing excessive movement of the tympanic membrane, contraction of the tensor tympani muscle (attached to the malleus) and/or the stapedius muscle (attached to the stapes) dampens the vibrations of the ossicles and decreases the force of the vibrations reaching the oval window. |
The temporal and infratemporal fossae are interconnected spaces on the lateral side of the head (Fig. 8.135). Their boundaries are formed by bone and soft tissues.
The temporal fossa is superior to the infratemporal fossa, above the zygomatic arch, and communicates with the infratemporal fossa below through the gap between the zygomatic arch and the more medial surface of the skull.
The infratemporal fossa is a wedge-shaped space deep to the masseter muscle and the underlying ramus of the mandible. Structures that travel between the cranial cavity, neck, pterygopalatine fossa, floor of the oral cavity, floor of the orbit, temporal fossa, and superficial regions of the head pass through it.
Of the four muscles of mastication (masseter, temporalis, medial pterygoid, and lateral pterygoid) that move the lower jaw at the temporomandibular joint, one (masseter) is lateral to the infratemporal fossa, two (medial and lateral pterygoid) are in the infratemporal fossa, and one fills the temporal fossa.
Bones that contribute significantly to the boundaries of the temporal and infratemporal fossae include the temporal, zygomatic, and sphenoid bones, and the maxilla and mandible (Figs. 8.136 and 8.137).
Parts of the frontal and parietal bones are also involved.
The squamous part of the temporal bone forms part of the bony framework of the temporal and infratemporal fossae.
The tympanic part of the temporal bone forms the posteromedial corner of the roof of the infratemporal fossa, and also articulates with the head of the mandible to form the temporomandibular joint.
The lateral surface of the squamous part of the temporal bone is marked by two surface features on the medial wall of the temporal fossa: a transversely oriented supramastoid crest, which extends posteriorly from the base of the zygomatic process and marks the posteroinferior border of the temporal fossa; and a vertically oriented groove for the middle temporal artery, a branch of the superficial temporal artery.
Two features that participate in forming the temporomandibular joint on the inferior aspect of the root of the zygomatic process are the articular tubercle and the mandibular fossa. Both are elongate from medial to lateral. Posterior to the mandibular fossa is the external acoustic meatus. The tympanic part of the temporal bone is a flat concave plate of bone that curves inferiorly from the back of the mandibular fossa and forms part of the wall of the external auditory meatus.
When viewed from inferiorly, there is a distinct tympanosquamous fissure between the tympanic and squamous parts of the temporal bone. Medially, a small slip of bone from the petrous part of the temporal bone insinuates itself into the fissure and forms a petrotympanic fissure between it and the tympanic part (Fig. 8.136).
The chorda tympani nerve exits the skull and enters the infratemporal fossa through the medial end of the petrotympanic fissure.
The parts of the sphenoid bone that form part of the bony framework of the infratemporal fossa are the lateral plate of the pterygoid process and the greater wing (Fig. 8.136). The greater wing also forms part of the medial wall of the temporal fossa.
The greater wings extend one on each side from the body of the sphenoid. They project laterally from the body and curve superiorly. The inferior and lateral surfaces form the roof of the infratemporal fossa and the medial wall of the temporal fossa, respectively. |
The sharply angled boundary between the lateral and inferior surfaces of the greater wing is the infratemporal crest (Fig. 8.136). Two apertures (the foramen ovale and the foramen spinosum) pass through the base of the greater wing and allow the mandibular nerve [V3] and the middle meningeal artery, respectively, to pass between the middle cranial fossa and infratemporal fossa. In addition, one or more small sphenoidal emissary foramina penetrate the base of the greater wing anteromedial to the foramen ovale and allow emissary veins to pass between the pterygoid plexus of veins in the infratemporal fossa and the cavernous sinus in the middle cranial fossa.
Projecting vertically downward from the greater wing immediately medial to the foramen spinosum is the irregularly shaped spine of the sphenoid, which is the attachment site for the cranial end of the sphenomandibular ligament.
The lateral plate of the pterygoid process is a vertically oriented sheet of bone that projects posterolaterally from the pterygoid process (Fig. 8.136). Its lateral and medial surfaces provide attachment for the lateral and medial pterygoid muscles, respectively.
The posterior surface of the maxilla contributes to the anterior wall of the infratemporal fossa (Fig. 8.136). This surface is marked by a foramen for the posterosuperior alveolar nerve and vessels. The superior margin forms the inferior border of the inferior orbital fissure.
The zygomatic bone is a quadrangular-shaped bone that forms the palpable bony prominence of the cheek:
A maxillary process extends anteromedially to articulate with the zygomatic process of the maxilla.
A frontal process extends superiorly to articulate with the zygomatic process of the frontal bone.
A temporal process extends posteriorly to articulate with the zygomatic process of the temporal bone to complete the zygomatic arch.
A small zygomaticofacial foramen on the lateral surface of the zygomatic bone transmits the zygomaticofacial nerve and vessels onto the cheek.
A thin plate of bone extends posteromedially from the frontal process and contributes to the lateral wall of the orbit on one side and the anterior wall of the temporal fossa on the other. A zygomaticotemporal foramen on the temporal fossa surface of the plate where it attaches to the frontal process is for the zygomaticotemporal nerve.
Ramus of mandible
The ramus of the mandible is quadrangular in shape and has medial and lateral surfaces and condylar and coronoid processes (Fig. 8.137).
The lateral surface of the ramus of the mandible is generally smooth except for the presence of a few obliquely oriented ridges. Most of the lateral surface provides attachment for the masseter muscle.
The posterior and inferior borders of the ramus intersect to form the angle of the mandible, while the superior border is notched to form the mandibular notch. The anterior border is sharp and is continuous below with the oblique line on the body of the mandible.
The coronoid process extends superiorly from the junction of the anterior and superior borders of the ramus. It is a flat, triangular process that provides attachment for the temporalis muscle.
The condylar process extends superiorly from the posterior and superior borders of the ramus. It consists of: the head of the mandible, which is expanded medially and participates in forming the temporomandibular joint; and the neck of the mandible, which bears a shallow depression (the pterygoid fovea) on its anterior surface for attachment of the lateral pterygoid muscle.
The medial surface of the ramus of the mandible is the lateral wall of the infratemporal fossa (Fig. 8.137B). Its most distinctive feature is the mandibular foramen, which is the superior opening of the mandibular canal. The inferior alveolar nerve and vessels pass through this foramen. |
Immediately anterosuperior to the mandibular foramen is a triangular elevation (the lingula) for attachment of the mandibular end of the sphenomandibular ligament.
An elongate groove (the mylohyoid groove) extends anteroinferiorly from the mandibular foramen. The nerve to the mylohyoid is in this groove.
Posteroinferior to the mylohyoid groove and mandibular foramen, the medial surface of the ramus of the mandible is roughened for attachment of the medial pterygoid muscle.
The temporomandibular joints, one on each side, allow opening and closing of the mouth and complex chewing or side-to-side movements of the lower jaw.
Each joint is synovial and is formed between the head of the mandible and the articular fossa and articular tubercle of the temporal bone (Fig. 8.138A).
Unlike most other synovial joints where the articular surfaces of the bones are covered by a layer of hyaline cartilage, those of the temporomandibular joint are covered by fibrocartilage. In addition, the joint is completely divided by a fibrous articular disc into two parts:
The lower part of the joint allows mainly the hinge-like depression and elevation of the mandible.
The upper part of the joint allows the head of the mandible to translocate forward (protrusion) onto the articular tubercle and backward (retraction) into the mandibular fossa.
Opening the mouth involves both depression and protrusion (Fig. 8.138B).
The forward or protrusive movement allows greater depression of the mandible by preventing backward movement of the angle of the mandible into structures in the neck.
The synovial membrane of the joint capsule lines all nonarticular surfaces of the upper and lower compartments of the joint and is attached to the margins of the articular disc.
The fibrous membrane of the joint capsule encloses the temporomandibular joint complex and is attached: above along the anterior margin of the articular tubercle, laterally and medially along the margins of the articular fossa, posteriorly to the region of the tympanosquamous suture, and below around the upper part of the neck of the mandible.
The articular disc attaches around its periphery to the inner aspect of the fibrous membrane.
Three extracapsular ligaments are associated with the temporomandibular joint—the lateral, sphenomandibular, and the stylomandibular ligaments (Fig. 8.139):
The lateral ligament is closest to the joint, just lateral to the capsule, and runs diagonally backward from the margin of the articular tubercle to the neck of the mandible.
The sphenomandibular ligament is medial to the temporomandibular joint, runs from the spine of the sphenoid bone at the base of the skull to the lingula on the medial side of the ramus of the mandible.
The stylomandibular ligament passes from the styloid process of the temporal bone to the posterior margin and angle of the mandible.
Movements of the mandible
A chewing or grinding motion occurs when the movements at the temporomandibular joint on one side are coordinated with a reciprocal set of movements at the joint on the other side. Movements of the mandible include depression, elevation, protrusion, and retraction (Fig. 8.140):
Depression is generated by the digastric, geniohyoid, and mylohyoid muscles on both sides, is normally assisted by gravity, and, because it involves forward movement of the head of the mandible onto the articular tubercle, the lateral pterygoid muscles are also involved.
Elevation is a very powerful movement generated by the temporalis, masseter, and medial pterygoid muscles and also involves movement of the head of the mandible into the mandibular fossa.
Protraction is mainly achieved by the lateral pterygoid muscle, with some assistance by the medial pterygoid. |
Retraction is carried out by the geniohyoid and digastric muscles, and by the posterior and deep fibers of the temporalis and masseter muscles, respectively.
Except for the geniohyoid muscle, which is innervated by the C1 spinal nerve, all muscles that move the temporomandibular joints are innervated by the mandibular nerve [V3] by branches that originate in the infratemporal fossa.
The masseter muscle is a powerful muscle of mastication that elevates the mandible (Fig. 8.141 and Table 8.11). It overlies the lateral surface of the ramus of the mandible.
The masseter muscle is quadrangular in shape and is anchored above to the zygomatic arch and below to most of the lateral surface of the ramus of the mandible.
The more superficial part of the masseter originates from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic process of the maxilla. It inserts into the angle of the mandible and related posterior part of the lateral surface of the ramus of the mandible.
The deep part of the masseter originates from the medial aspect of the zygomatic arch and the posterior part of its inferior margin and inserts into the central and upper part of the ramus of the mandible as high as the coronoid process.
The masseter is innervated by the masseteric nerve from the mandibular nerve [V3] and supplied with blood by the masseteric artery from the maxillary artery.
The masseteric nerve and artery originate in the infratemporal fossa and pass laterally over the margin of the mandibular notch to enter the deep surface of the masseter muscle.
The temporal fossa is a narrow fan-shaped space that covers the lateral surface of the skull (Fig. 8.142A):
Its upper margin is defined by a pair of temporal lines that arch across the skull from the zygomatic process of the frontal bone to the supramastoid crest of the temporal bone.
It is limited laterally by the temporal fascia, which is a tough, fan-shaped aponeurosis overlying the temporalis muscle and attached by its outer margin to the superior temporal line and by its inferior margin to the zygomatic arch.
Anteriorly, it is limited by the posterior surface of the frontal process of the zygomatic bone and the posterior surface of the zygomatic process of the frontal bone, which separate the temporal fossa behind from the orbit in front.
Its inferior margin is marked by the zygomatic arch laterally and by the infratemporal crest of the greater wing of the sphenoid medially (Fig. 8.142B)—between these two features, the floor of the temporal fossa is open medially to the infratemporal fossa and laterally to the region containing the masseter muscle.
The major structure in the temporal fossa is the temporalis muscle.
Also passing through the fossa is the zygomaticotemporal branch of the maxillary nerve [V2], which enters the region through the zygomaticotemporal foramen on the temporal fossa surface of the zygomatic bone.
The temporalis muscle is a large, fan-shaped muscle that fills much of the temporal fossa (Fig. 8.143). It originates from the bony surfaces of the fossa superiorly to the inferior temporal line and is attached laterally to the surface of the temporal fascia. The more anterior fibers are oriented vertically while the more posterior fibers are oriented horizontally. The fibers converge inferiorly to form a tendon, which passes between the zygomatic arch and the infratemporal crest of the greater wing of the sphenoid to insert on the coronoid process of the mandible.
The temporalis muscle attaches down the anterior surface of the coronoid process and along the related margin of the ramus of the mandible, almost to the last molar tooth. |
The temporalis is a powerful elevator of the mandible. Because this movement involves posterior translocation of the head of the mandible from the articular tubercle of the temporal bone and back into the mandibular fossa, the temporalis also retracts the mandible or pulls it posteriorly. In addition, the temporalis participates in side-to-side movements of the mandible.
The temporalis is innervated by deep temporal nerves that originate from the mandibular nerve [V3] in the infratemporal fossa and then pass into the temporal fossa.
Blood supply of the temporalis is by deep temporal arteries, which travel with the nerves, and the middle temporal artery, which penetrates the temporal fascia at the posterior end of the zygomatic arch.
The deep temporal nerves, usually two in number, originate from the anterior trunk of the mandibular nerve [V3] in the infratemporal fossa (Fig. 8.144). They pass superiorly and around the infratemporal crest of the greater wing of the sphenoid to enter the temporal fossa deep to the temporalis muscle, and supply the temporalis muscle.
The zygomaticotemporal nerve is a branch of the zygomatic nerve (see Fig. 8.87, p. 922). The zygomatic nerve is a branch of the maxillary nerve [V2], which originates in the pterygopalatine fossa and passes into the orbit.
The zygomaticotemporal nerve enters the temporal fossa through one or more small foramina on the temporal fossa surface of the zygomatic bone.
Branches of the zygomaticotemporal nerve pass superiorly between the bone and the temporalis muscle to penetrate the temporal fascia and supply the skin of the temple (Fig. 8.144).
Normally two in number, these vessels originate from the maxillary artery in the infratemporal fossa and travel with the deep temporal nerves around the infratemporal crest of the greater wing of the sphenoid to supply the temporalis muscle (Fig. 8.144). They anastomose with branches of the middle temporal artery.
The middle temporal artery originates from the superficial temporal artery just superior to the root of the zygomatic arch between this structure and the external ear (Fig. 8.144). It penetrates the temporalis fascia, passes under the margin of the temporalis muscle, and travels superiorly on the deep surface of the temporalis muscle.
The middle temporal artery supplies the temporalis and anastomoses with branches of the deep temporal arteries.
The wedge-shaped infratemporal fossa is inferior to the temporal fossa and between the ramus of the mandible laterally and the wall of the pharynx medially. It has a roof, a lateral wall, and a medial wall, and is open to the neck posteroinferiorly (Fig. 8.145):
The roof is formed by the inferior surfaces of the greater wing of the sphenoid and the temporal bone, contains the foramen spinosum, foramen ovale, and the petrotympanic fissure, and lateral to the infratemporal crest of the greater wing of the sphenoid, is open superiorly to the temporal fossa.
The lateral wall is the medial surface of the ramus of the mandible, which contains the opening to the mandibular canal.
The medial wall is formed anteriorly by the lateral plate of the pterygoid process and more posteriorly by the pharynx and by two muscles of the soft palate (tensor and levator veli palatini muscles), and contains the pterygomaxillary fissure anteriorly, which allows structures to pass between the infratemporal and pterygopalatine fossae.
The anterior wall is formed by part of the posterior surface of the maxilla and contains the alveolar foramen, and the upper part opens as the inferior orbital fissure into the orbit. |
Major contents of the infratemporal fossa include the sphenomandibular ligament, medial and lateral pterygoid muscles (Table 8.11), the maxillary artery, the mandibular nerve [V3], branches of the facial nerve [VII] and the glossopharyngeal nerve [IX], and the pterygoid plexus of veins.
The sphenomandibular ligament is an extracapsular ligament of the temporomandibular joint. It is attached superiorly to the spine of the sphenoid bone and expands inferiorly to attach to the lingula of the mandible and the posterior margin of the mandibular foramen (Fig. 8.146).
The medial pterygoid muscle is quadrangular in shape and has deep and superficial heads (Fig. 8.146):
The deep head is attached above to the medial surface of the lateral plate of the pterygoid process and the associated surface of the pyramidal process of the palatine bone, and descends obliquely downward, medial to the sphenomandibular ligament, to attach to the roughened medial surface of the ramus of the mandible near the angle of the mandible.
The superficial head originates from the tuberosity of the maxilla and adjacent pyramidal process of the palatine bone and joins with the deep head to insert on the mandible.
The medial pterygoid mainly elevates the mandible. Because it passes obliquely backward to insert into the mandible, it also assists the lateral pterygoid muscle in protruding the lower jaw.
The medial pterygoid is innervated by the nerve to the medial pterygoid from the mandibular nerve [V3].
The lateral pterygoid is a thick triangular muscle and like the medial pterygoid muscle has two heads (Fig. 8.147):
The upper head originates from the roof of the infratemporal fossa (inferior surface of the greater wing of the sphenoid and the infratemporal crest) lateral to the foramen ovale and foramen spinosum.
The lower head is larger than the upper head and originates from the lateral surface of the lateral plate of the pterygoid process, and the inferior part insinuates itself between the cranial attachments of the two heads of the medial pterygoid.
The fibers from both heads of the lateral pterygoid muscle converge to insert into the pterygoid fovea of the neck of the mandible and into the capsule of the temporomandibular joint in the region where the capsule is attached internally to the articular disc.
Unlike the medial pterygoid muscle whose fibers tend to be oriented vertically, those of the lateral pterygoid are oriented almost horizontally. As a result, when the lateral pterygoid contracts it pulls the articular disc and head of the mandible forward onto the articular tubercle and is therefore the major protruder of the lower jaw.
The lateral pterygoid is innervated by the nerve to the lateral pterygoid from the mandibular nerve [V3].
When the lateral and medial pterygoids contract on only one side, the chin moves to the opposite side. When opposite movements at the two temporomandibular joints are coordinated, a chewing movement results.
The mandibular nerve [V3] is the largest of the three divisions of the trigeminal nerve [V].
Unlike the ophthalmic [V1] and maxillary [V2] nerves, which are purely sensory, the mandibular nerve [V3] is both motor and sensory. |
In addition to carrying general sensation from the teeth and gingivae of the mandible, the anterior two-thirds of the tongue, mucosa on the floor of the oral cavity, the lower lip, skin over the temple and lower face, and part of the cranial dura mater, the mandibular nerve [V3] also carries motor innervation to most of the muscles that move the mandible, one of the muscles (tensor tympani) in the middle ear, and one of the muscles of the soft palate (tensor veli palatini).
All branches of the mandibular nerve [V3] originate in the infratemporal fossa.
Like the ophthalmic [V1] and maxillary [V2] nerves, the sensory part of the mandibular nerve [V3] originates from the trigeminal ganglion in the middle cranial fossa (Fig. 8.148):
The sensory part of the mandibular nerve [V3] drops vertically through the foramen ovale and enters the infratemporal fossa between the tensor veli palatini muscle and the upper head of the lateral pterygoid muscle.
The small motor root of the trigeminal nerve [V] passes medial to the trigeminal ganglion in the cranial cavity, then passes through the foramen ovale and immediately joins the sensory part of the mandibular nerve [V3].
Soon after the sensory and motor roots join, the mandibular nerve [V3] gives rise to a small meningeal branch and to the nerve to the medial pterygoid, and then divides into anterior and posterior trunks (Fig. 8.148):
Branches from the anterior trunk are the buccal, masseteric, and deep temporal nerves, and the nerve to the lateral pterygoid, all of which, except the buccal nerve (which is predominantly sensory) are motor nerves.
Branches from the posterior trunk are the auriculotemporal, lingual, and inferior alveolar nerves, all of which, except a small nerve (nerve to the mylohyoid) that branches from the inferior alveolar nerve, are sensory nerves.
The meningeal branch originates from the medial side of the mandibular nerve [V3] and ascends to leave the infratemporal fossa with the middle meningeal artery and reenter the cranial cavity through the foramen spinosum (Fig. 8.148). It is sensory for the dura mater, mainly of the middle cranial fossa, and also supplies the mastoid cells that communicate with the middle ear.
Nerve to medial pterygoid
The nerve to the medial pterygoid also originates medially from the mandibular nerve [V3] (Fig. 8.148). It descends to enter and supply the deep surface of the medial pterygoid muscle. Near its origin from the mandibular nerve [V3], it has two small branches:
One of these supplies the tensor veli palatini.
The other ascends to supply the tensor tympani muscle, which occupies a small bony canal above and parallel to the pharyngotympanic tube in the temporal bone.
The buccal nerve is a branch of the anterior trunk of the mandibular nerve [V3] (Fig. 8.148). It is predominantly a sensory nerve, but may also carry the motor innervation to the lateral pterygoid muscle and to part of the temporalis muscle.
The buccal nerve passes laterally between the upper and lower heads of the lateral pterygoid and then descends around the anterior margin of the insertion of the temporalis muscle to the anterior margin of the ramus of the mandible, often slipping through the tendon of the temporalis. It continues into the cheek lateral to the buccinator muscle to supply general sensory nerves to the adjacent skin and oral mucosa and the buccal gingivae of the lower molars. |
The masseteric nerve is a branch of the anterior trunk of the mandibular nerve [V3] (Fig. 8.148; also see Fig. 8.141). It passes laterally over the lateral pterygoid muscle and through the mandibular notch to penetrate and supply the masseter muscle.
The deep temporal nerves, usually two in number, originate from the anterior trunk of the mandibular nerve [V3] (Fig. 8.148; also see Fig. 8.144). They pass laterally above the lateral pterygoid muscle and curve around the infratemporal crest to ascend in the temporal fossa and supply the temporalis muscle from its deep surface.
Nerve to lateral pterygoid
The nerve to the lateral pterygoid may originate directly as a branch from the anterior trunk of the mandibular nerve [V3] or from its buccal branch (Fig. 8.148). From its origin, it passes directly into the deep surface of the lateral pterygoid muscle.
The auriculotemporal nerve is the first branch of the posterior trunk of the mandibular nerve [V3] and originates as two roots, which pass posteriorly around the middle meningeal artery ascending from the maxillary artery to the foramen spinosum (Fig. 8.149).
The auriculotemporal nerve passes first between the tensor veli palatini muscle and the upper head of the lateral pterygoid muscle, and then between the sphenomandibular ligament and the neck of the mandible. It curves laterally around the neck of the mandible and then ascends deep to the parotid gland between the temporomandibular joint and ear.
The terminal branches of the auriculotemporal nerve carry general sensation from skin over a large area of the temple. In addition, the auriculotemporal nerve contributes to sensory innervation of the external ear, the external auditory meatus, tympanic membrane, and temporomandibular joint. It also delivers postganglionic parasympathetic nerves from the glossopharyngeal nerve [IX] to the parotid gland.
The lingual nerve is a major sensory branch of the posterior trunk of the mandibular nerve [V3] (Fig. 8.149A,B). It carries general sensation from the anterior two-thirds of the tongue, oral mucosa on the floor of the oral cavity, and lingual gingivae associated with the lower teeth.
The lingual nerve is joined high in the infratemporal fossa by the chorda tympani branch of the facial nerve [VII] (Fig. 8.149C), which carries: taste from the anterior two-thirds of the tongue, and parasympathetic fibers to all salivary glands below the level of the oral fissure.
The lingual nerve first descends between the tensor veli palatini muscle and the lateral pterygoid muscle, where it is joined by the chorda tympani nerve, and then descends across the lateral surface of the medial pterygoid muscle to enter the oral cavity.
The lingual nerve enters the oral cavity between the posterior attachment of the mylohyoid muscle to the mylohyoid line and the attachment of the superior constrictor of the pharynx to the pterygomandibular raphe. As the lingual nerve enters the floor of the oral cavity, it is in a shallow groove on the medial surface of the mandible immediately inferior to the last molar tooth.
In this position, it is palpable through the oral mucosa and in danger when one is operating on the molar teeth and gingivae (Fig. 8.149C). |
The lingual nerve passes into the tongue on the lateral surface of the hyoglossus muscle where it is attached to the submandibular ganglion. This ganglion is where the preganglionic parasympathetic fibers carried from the infratemporal fossa into the floor of the oral cavity on the lingual nerve synapse with postganglionic parasympathetic fibers (see Fig. 8.150).
The inferior alveolar nerve, like the lingual nerve, is a major sensory branch of the posterior trunk of the mandibular nerve [V3] (Fig. 8.149A–C). In addition to innervating all lower teeth and much of the associated gingivae, it also supplies the mucosa and skin of the lower lip and skin of the chin. It has one motor branch, which innervates the mylohyoid muscle and the anterior belly of the digastric muscle.
The inferior alveolar nerve originates deep to the lateral pterygoid muscle from the posterior trunk of the mandibular nerve [V3] in association with the lingual nerve. It descends on the lateral surface of the medial pterygoid muscle, passes between the sphenomandibular ligament and the ramus of the mandible, and then enters the mandibular canal through the mandibular foramen. Just before entering the mandibular foramen, it gives origin to the nerve to the mylohyoid (Fig. 8.149C), which lies in the mylohyoid groove inferior to the foramen and continues anteriorly below the floor of the oral cavity to innervate the mylohyoid muscle and the anterior belly of the digastric muscle.
The inferior alveolar nerve passes anteriorly within the mandibular canal of the lower jaw. The mandibular canal and its contents are inferior to the roots of the molar teeth, and the roots can sometimes curve around the canal making extraction of these teeth difficult.
The inferior alveolar nerve supplies branches to the three molar teeth and the second premolar tooth and associated labial gingivae, and then divides into its two terminal branches: the incisive nerve, which continues in the mandibular canal to supply the first premolar, incisor, and canine teeth, and related gingivae; and the mental nerve, which exits the mandible through the mental foramen and supplies the lower lip and chin (Fig. 8.149A,B). The mental nerve is palpable and sometimes visible through the oral mucosa adjacent to the roots of the premolar teeth.
Chorda tympani and the lesser petrosal nerve
Branches of two cranial nerves join branches of the mandibular nerve [V3] in the infratemporal fossa (Fig. 8.150). These are the chorda tympani branch of the facial nerve [VII] and the lesser petrosal nerve, a branch of the tympanic plexus in the middle ear, which had its origin from a branch of the glossopharyngeal nerve [IX] (see Fig. 8.125, p. 953).
The chorda tympani (Fig. 8.150) carries taste from the anterior two-thirds of the tongue and parasympathetic innervation to all salivary glands below the level of the oral fissure.
The chorda tympani originates from the facial nerve [VII] within the temporal bone and in association with the mastoid wall of the middle ear, passes anteriorly through a small canal, and enters the lateral aspect of the middle ear. As it continues anterosuperiorly across the middle ear, it is separated from the tympanic membrane by the handle of the malleus. It leaves the middle ear through the medial end of the petrotympanic fissure, enters the infratemporal fossa, descends medial to the spine of the sphenoid and then to the lateral pterygoid muscle, and joins the lingual nerve. |
Preganglionic parasympathetic fibers carried in the chorda tympani synapse with postganglionic parasympathetic fibers in the submandibular ganglion, which “hangs off” the lingual nerve in the floor of the oral cavity (Fig. 8.150).
Postganglionic parasympathetic fibers leave the submandibular ganglion and either: reenter the lingual nerve to travel with its terminal branches to reach target tissues, or pass directly from the submandibular ganglion into glands (Fig. 8.150).
The taste (SA) fibers do not pass through the ganglion and are distributed with terminal branches of the lingual nerve.
The lesser petrosal nerve carries mainly parasympathetic fibers destined for the parotid gland (Fig. 8.150). The preganglionic parasympathetic fibers are located in the glossopharyngeal nerve [IX] as it exits the jugular foramen at the base of the skull. Branching from the glossopharyngeal nerve [IX] either within or immediately outside the jugular foramen is the tympanic nerve (Fig. 8.150B).
The tympanic nerve reenters the temporal bone through a small foramen on the ridge of bone separating the jugular foramen from the carotid canal and ascends through a small bony canal (inferior tympanic canaliculus) to the promontory located on the labyrinthine (medial) wall of the middle ear. Here it participates in the formation of the tympanic plexus. The lesser petrosal nerve is a branch of this plexus (Fig. 8.150B).
The lesser petrosal nerve contains mainly preganglionic parasympathetic fibers. It leaves the middle ear and enters the middle cranial fossa through a small opening on the anterior surface of the petrous part of the temporal bone just lateral and inferior to the opening for the greater petrosal nerve, a branch of the facial nerve [VII]. The lesser petrosal nerve then passes medially and descends through the foramen ovale with the mandibular nerve [V3].
In the infratemporal fossa, the preganglionic parasympathetic fibers synapse with cell bodies of postganglionic parasympathetic fibers in the otic ganglion located on the medial side of the mandibular nerve [V3] around the origin of the nerve to the medial pterygoid. Postganglionic parasympathetic fibers leave the otic ganglion and join the auriculotemporal nerve, which carries them to the parotid gland.
The maxillary artery is the largest branch of the external carotid artery in the neck and is a major source of blood supply for the nasal cavity, the lateral wall and roof of the oral cavity, all teeth, and the dura mater in the cranial cavity. It passes through and supplies the infratemporal fossa and then enters the pterygopalatine fossa, where it gives origin to terminal branches (Fig. 8.151).
The maxillary artery originates within the substance of the parotid gland and then passes forward, between the neck of the mandible and sphenomandibular ligament, into the infratemporal fossa. It ascends obliquely through the infratemporal fossa to enter the pterygopalatine fossa by passing through the pterygomaxillary fissure. This part of the vessel may pass either lateral or medial to the lower head of the lateral pterygoid. If it passes medial to the lower head, the maxillary artery then loops laterally between the upper and lower heads of the lateral pterygoid to access the pterygomaxillary fissure.
Branches of the maxillary artery are as follows (Fig. 8.151): |
The first part of the maxillary artery (the part between the neck of the mandible and the sphenomandibular ligament) gives origin to two major branches (the middle meningeal and inferior alveolar arteries) and a number of smaller branches (deep auricular, anterior tympanic, and accessory meningeal).
The second part of the maxillary artery (the part related to the lateral pterygoid muscle) gives origin to deep temporal, masseteric, buccal, and pterygoid branches, which course with branches of the mandibular nerve [V3].
The third part of the maxillary artery is in the pterygopalatine fossa (see Fig. 8.158)
The middle meningeal artery ascends vertically from the maxillary artery and passes through the foramen spinosum to enter the cranial cavity (Fig. 8.151). In the infratemporal fossa, it passes superiorly between the sphenomandibular ligament on the medial side and the lateral pterygoid muscle on the lateral side. Just inferior to the foramen spinosum, it passes between the two roots of the auriculotemporal nerve at their origin from the mandibular nerve [V3] (Fig. 8.151).
The middle meningeal artery is the largest of the meningeal vessels and supplies much of the dura mater, bone, and related bone marrow of the cranial cavity walls.
Within the cranial cavity, the middle meningeal artery and its branches travel in the periosteal (outer) layer of dura mater, which is tightly adherent to the bony walls. As major branches of the middle meningeal artery pass superiorly up the walls of the cranial cavity, they can be damaged by lateral blows to the head. When the vessels are torn, the leaking blood, which is under arterial pressure, slowly separates the dura mater from its attachment to the bone, resulting in an extradural hematoma.
The inferior alveolar artery descends from the maxillary artery to enter the mandibular foramen and canal with the inferior alveolar nerve (Fig. 8.151). It is distributed with the inferior alveolar nerve and supplies all lower teeth, and contributes to the supply of the buccal gingivae, chin, and lower lip.
Before entering the mandible, the inferior alveolar artery gives origin to a small mylohyoid branch, which accompanies the nerve to the mylohyoid.
Deep auricular, anterior tympanic, and accessory meningeal arteries
The deep auricular, anterior tympanic, and accessory meningeal arteries are small branches from the first part of the maxillary artery and contribute to the blood supply of the external acoustic meatus, deep surface of the tympanic membrane, and cranial dura mater, respectively.
The accessory meningeal branch also contributes small branches to surrounding muscles in the infratemporal fossa before ascending through the foramen ovale into the cranial cavity to supply the dura mater.
Branches from the second part
Deep temporal arteries, usually two in number, originate from the second part of the maxillary artery and travel with the deep temporal nerves to supply the temporalis muscle in the temporal fossa (Fig. 8.151).
Numerous pterygoid arteries also originate from the second part of the maxillary artery and supply the pterygoid muscles.
The masseteric artery, also from the second part of the maxillary artery, accompanies the masseteric nerve laterally through the mandibular notch to supply the masseter muscle.
The buccal artery is distributed with the buccal nerve and supplies skin, muscle, and oral mucosa of the cheek.
The pterygoid plexus is a network of veins between the medial and lateral pterygoid muscles, and between the lateral pterygoid and temporalis muscles (Fig. 8.152). |
Veins that drain regions supplied by arteries branching from the maxillary artery in the infratemporal fossa and pterygopalatine fossa connect with the pterygoid plexus. These tributary veins include those that drain the nasal cavity, roof and lateral wall of the oral cavity, all teeth, muscles of the infratemporal fossa, paranasal sinuses, and nasopharynx. In addition, the inferior ophthalmic vein from the orbit can drain through the inferior orbital fissure into the pterygoid plexus.
Significantly, small emissary veins often connect the pterygoid plexus in the infratemporal fossa to the cavernous sinus in the cranial cavity. These emissary veins, which pass through the foramen ovale, through the cartilage that fills the foramen lacerum, and through a small sphenoidal foramen on the medial side of the lateral plate of the pterygoid process at the base of the skull, are a route by which infections can spread into the cranial cavity from structures, such as the teeth, that are drained by the pterygoid plexus. Also, because there are no valves in veins of the head and neck, anesthetic inadvertently injected under pressure into veins of the pterygoid plexus can backflow into tissues or into the cranial cavity.
The pterygoid plexus connects: posteriorly, via a short maxillary vein, with the retromandibular vein in the neck; and anteriorly, via a deep facial vein, with the facial vein on the face.
The pterygopalatine fossa is an inverted teardrop-shaped space between bones on the lateral side of the skull immediately posterior to the maxilla (Fig. 8.153).
Although small in size, the pterygopalatine fossa communicates via fissures and foramina in its walls with the: middle cranial fossa, infratemporal fossa, floor of the orbit, lateral wall of the nasal cavity, oropharynx, and roof of the oral cavity.
Because of its strategic location, the pterygopalatine fossa is a major site of distribution for the maxillary nerve [V2] and for the terminal part of the maxillary artery. It also contains the pterygopalatine ganglion where preganglionic parasympathetic fibers originating in the facial nerve [VII] synapse with postganglionic parasympathetic fibers and these fibers, along with sympathetic fibers originating from the T1 spinal cord level join branches of the maxillary nerve [V2].
All the upper teeth receive their innervation and blood supply from the maxillary nerve [V2] and the terminal part of the maxillary artery, respectively, that pass through the pterygopalatine fossa.
The walls of the pterygopalatine fossa are formed by parts of the palatine, maxilla, and sphenoid bones (Fig. 8.153):
The anterior wall is formed by the posterior surface of the maxilla.
The medial wall is formed by the lateral surface of the palatine bone.
The posterior wall and roof are formed by parts of the sphenoid bone.
The part of the sphenoid bone that contributes to the formation of the pterygopalatine fossa is the anterosuperior surface of the pterygoid process (Fig. 8.154). Opening onto this surface are two large foramina:
The maxillary nerve [V2] passes through the most lateral and superior of these—the foramen rotundum—which communicates posteriorly with the middle cranial fossa (Fig. 8.154B).
The greater petrosal nerve from the facial nerve [VII] and sympathetic fibers from the internal carotid plexus join to form the nerve of the pterygoid canal that passes forward into the pterygopalatine fossa through the more medial and inferior foramen—the anterior opening of the pterygoid canal. |
Subsets and Splits