CEREBRO-SPINAL NERVES 401 



on the side of the chest beneath the panniculus and above the spur vein, 

 whose course it follows, to be lost in the panniculus of the flank. It is 

 formed mainly of the dorsal roots of the thoracic plexus, and to a small 

 extent from the eighth cervical nerve. In its course backwards it gives 

 off branches which anastomose with the second and third perforating 

 intercostal nerves, and forms a net-work over the inner surface of the 

 panniculus. The panniculus extending over the shoulder and arm receives 

 fibres from this nerve. 



Circumflex or Axillary Nerve. — This is a nerve of considerable 

 size; it is derived from the seventh and eighth cervical roots, and after 

 crossing the subscapularis soon enters the interspace between that muscle 

 and teres major. It then passes behind the shoulder joint, accompanied 

 by the posterior circumflex artery, and distributes its branches to the teres 

 minor deltoid, mastoido-humeralis, and ultimately reaches the integument 

 in front of the arm. 



Behind the shoulder it gives small twigs to the scapulo-humeralis 

 posticus. 



Dorsal Nerves, eighteen pairs. — These nerves on issuing from the 

 spinal canal divide into two sets of branches, as we saw occur in the case 

 of the cervical nerves. The upper divisions, which are the smaller, ascend 

 to reach the dorsal muscles and skin of the back, to both of which they 

 are distributed. The inferior divisions descend, and having gained the 

 intercostal spaces, pass downwards along the posterior border of the ribs 

 beneath the pleura as the intercostal nerves. 



In their course they give branches to the panniculus and skin, and 

 the first seven or eight terminate in the pectoral muscles and skin cover- 

 ing them, and the last ten are distributed to the rectus abdominis, the 

 transversalis abdominis, and the skin of the belly. The first and second 

 intercostal nerves send branches to the brachial plexus from their inferior 

 divisions. 



Lumbar Nerves, six pairs. — The lumbar nerves, like the dorsal, 

 divide, after leaving the spinal cord, into a superior and inferior branch. 

 The former, passing in an upward direction, ramify through to the muscles 

 of the loins, and ultimately reach the skin, where they terminate. The 

 inferior branches are variously distributed. Those of the first two, after 

 supplying the psoas magnus, pass over the edge of that muscle, and are 

 distributed to the muscles of the flank, the skin, and some fine filaments 

 to tlie muscles of the thigh. The inferior branch of the third nerve 

 supplies the psoas magnus, psoas parvus, and quadratus lumborum, and 

 its ultimate fibres are expended in the skin of the thigh. The fourth, 

 fifth, and sixth lumbar branches contribute to form the lumbo- sacral 



