in the intercostal spaces below the intercostal vessels. At the back of the chest they lie between the pleura and the posterior intercostal membranes, but soon they run between the internal intercostals and the innermost intercostals then anteriorly they lie between the pleura and the internal intercostals. Near the sternum, they cross in front of the internal mammary artery and transversus thoracis muscle, pierce the intercostales interni, the anterior intercostal membranes, and pectoralis major, and supply the integument of the front of the thorax and over the mammary gland, forming the anterior cutaneous branches of the thorax; the branch from the second nerve unites with the anterior supraclavicular nerves of the cervical plexus. The fourth intercostal nerve is innervated by cutaneous slowly-adapting and rapidly-adapting mechanoreceptors, especially by ones densely-packed under the areola; innervation subsequently triggers oxytocin release, which, when in the peripheral bloodstream, causes myoepithelial cell contraction and lactation: this is an example of a non-nerve-innervation muscular reflex. Branches Numerous slender muscular filaments supply the Intercostales, the Subcostales, the Levatores costarum, the Serratus posterior superior, and the Transversus thoracis. At the front of the thorax some of these branches cross the costal cartilages from one intercostal space to another. Lateral cutaneous branches (rami cutanei laterales) are derived from the intercostal nerves, about midway between the vertebræ and sternum; they pierce the Intercostales externi and Serratus anterior, and divide into anterior and posterior branches. The anterior branches run forward to the side and the forepart of the chest and skin, fourth nerve anterior branches supplying the areola and the mamma; those of the fifth and sixth nerves supply the upper digitations of the Obliquus externus abdominis. The posterior branches run backward, and supply the skin over the scapula and Latissimus dorsi. The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is named the intercostobrachial nerve. The lower thoracic nerves: 7th–11th The lower thoracic nerves: 12th Anterior division Lateral cutaneous branch The lateral cutaneous branch of the last thoracic nerve is large, and undivided. It perforates the internal and the external oblique muscles, descends over the iliac crest in front of the lateral cutaneous branch of the iliohypogastric nerve, and is distributed to the skin of the front part of the gluteal muscles, some of its filaments extending as low as the greater trochanter of the femur. Additional