<prompt> Chief inspiratory muscle is:DiaphragmPectoralis majorPectoralis minorExternal intercostals  <response>: Ans: a Diaphragm Ref: BDC, 4th ed, Vol. II, p. 311Diaphragm is the chief muscle of inspiration. On contraction, it descends, increasing the vertical diameter of the thorax. Max. excursion: 6-10 cmDiaphragmNerve supply: Motor: Phrenic nerve C-3, 4, 5Sensory: Lower six thoracic nervesActions: 1 Principal muscle of inspiration2 Acts in all expulsive acts to give additional power3 Right crus has a sphincteric action on the lower end of the oesophagus.Structures passing through the DiaphragmT12- Aortic openingT10- Oesophageal openingT8- Vena caval opningAortaAzygos veinThoracis ductOesophagusVagus nerveEsophageal branch of leftGastric arteryIVCRt. phrenic nerveSmall openings Each crus is pierced by the greater and lesser splanchnic nerves Lt. crus is pierced by the a hemiazygos vein b Lt. phrenic nerve Sympathetic chain- behind the medial arcuate ligament Subcostal nerves and vessels- behind the lateral arcuate ligament Larry sSpace Space of Morgagni- Superior epigastric vessels; this space lies between the xiphoid process and costal cartilage Musculophrenic vessels- pierce at the level of the 8th and 9th costal cartilage 