760 



SPINAL NERVES. 



teres minor, and between the huinerus and 

 long head of the triceps to terminate in the 

 deep surface of the deltoid. It gives off 

 in this course branches to the subscapularis 

 and teres minor; that for the latter entering 

 the lower border of the muscle, and prior 

 to dividing into its deltoid branches. The 

 cutaneous nerve of the shoulder passes from 

 behind the posterior border of the deltoid, 

 perforates the fascia, and divides into a series 

 of radiating branches, which supply the skin 

 at the upper and back part of the shoulder. 

 The deltoid branches ramify through the sub- 

 stance of the muscle as far as its insertion, 

 and from one of them a filament is given off to 

 the capsular ligament of the shoulder joint. 



The anterior branches of the dorsal (inter- 

 costal) nerves are twelve in number, the first 

 escaping between the first and second dorsal 

 vertebras, and the last between the last dor- 

 sal and first lumbar. They run more or 

 less parallel to each other without forming 

 plexuses, and are destined to supply the tho- 

 racic and abdominal parietes, and the skin 

 about the arm and axilla. They present 

 general and special characters. Each branch 

 runs outwards, from its origin, being sepa- 

 rated from the posterior root by the in- 

 tervention of the anterior costo-transverse 

 ligament, to reach the intercostal space, be- 

 tween the pleura and external layer of the in- 

 tercostal muscles, and below the intercostal 

 vessels. Having communicated by one or two 

 filaments with the thoracic ganglia of the 

 sympathetic, these nerves are continued be- 

 tween the two layers of the intercostals, to 

 about midway between the spine and the 

 sternum, and here they divide into cutaneous 

 and intercostal branches. The cutaneous 

 branches perforate, in a very oblique manner, 

 the external layer of intercostals ; and, after a 

 short course, forwards and outwards, between 

 them and the serratus magnus, either escape 

 between the digitations of the serratus mag- 

 nus and external oblique, or perforate their 

 fibres, and divide into anterior and posterior 

 branches. This division takes place some- 

 times when the trunks of the cutaneous nerves 

 are covered by the serratus and oblique. The 

 posterior branches are reflected backwards and 

 upwards, and, after a course of an inch or 

 two between the latissimus dorsi and the skin, 

 terminate in the latter. The anterior branches 

 are directed downwards and forwards, or 

 horizontally, and, after a longer course than 

 the posterior branches, terminate, like them, 

 in the skin. 



The intercostal branches, though somewhat 

 smaller than the cutaneous, represent the con- 

 tinuation of the anterior branches of the 

 dorsal nerves. They continue in the original 

 course of the latter, below the lower edge of 

 the ribs on the one hand, and the costal carti- 

 lages on the other ; and near the border of 

 the sternum above, and the linea alba below, 

 perforate the muscular fibres, and become 

 cutaneous. The trunks of the intercostal 

 nerves and their continuation give off numer- 

 ous filaments to the supply of the intercostal 



muscles, and several extremely delicate twigs, 

 which frequently pass over the inner aspect of 

 the ribs, to communicate above and below 

 with each other in the intercostal spaces. 



The special characters of the intercostal 

 nerves are as follow : 



The first dorsal nerve, ascending in front, 

 and across the neck, of the first rib, to assist 

 in the formation of the brachial plexus, gives 

 off only a small intercostal nerve. "This 

 comes away soon after the nerve has left the 

 intervertebral foramen, and is directed along 

 the inner surface of the first rib, to the first 

 intercostal space, without giving off a middle 

 cutaneous branch, and passes along the lower 

 edge of the cartilage to the sternum, by the 

 side of which it perforates the intercostal 

 muscles, and terminates on the skin, at the 

 upper and fore part of the thorax. 



The second dorsal nerve crosses obliquely 

 over the second rib, external to its neck, to 

 gain the lower part of the first intercostal 

 space, and again crosses the second rib, to 

 reach the second intercostal space on a level 

 with the middle of the former. Its cutaneous 

 branch is of large size, and, supplying the arm 

 with cutaneous branches, is named the inter- 

 costo-humeral, which perforates the second 

 intercostal space. In traversing the axilla it 

 gives off a branch of communication to the 

 accessory internal cutaneous, and one to com- 

 municate with the second intercosto-humeral ; 

 the latter united nerve sending filaments to 

 the skin at the upper and anterior part of the 

 arm. Two or three filaments represent the 

 termination of the nerve, cross the lower part 

 of the posterior boundary of the axilla, and 

 terminate in the skin, at the upper and back 

 part of the arm. 



The cutaneous branch of the third dorsal (the 

 second intercosto-humeral) is smaller than 

 the second, and passes through the third in- 

 tercostal space : it divides into an anterior 

 and posterior branch ; the former winds up- 

 wards, forwards, and inwards, over the lower 

 border of the pectoralis major, to terminate in 

 the mamma and integument ; the latter, having 

 communicated with the second intercostal, 

 sends filaments to the axilla, and terminal 

 branches, which are directed to the outer and 

 anterior part of the axilla to supply the skin, 

 at the upper and back part of the arm. 



The cutaneous branches of the fourth and fifth 

 dorsal nerves send filaments inwards, to supply 

 the mamma; and filaments backwards, over 

 the superficial surface of the latissimus dorsi, 

 to supply the skin over the anterior and outer 

 part of the scapula. The intercostal nerves 

 of the eighth, ninth, tenth, and eleventh dorsal 

 nerves perforate the intercostal spaces of the 

 false ribs, pass through the costal attachments 

 of the diaphragm, to get between the external 

 and internal oblique, as far as the border of 

 the rectus, where they give off' small cuta- 

 neous branches. Entering the sheath of the 

 rectus, they proceed along the posterior sur- 

 face of the muscle, and terminate, by giving 

 off some filaments, which ramify in its inner 

 part ; and others, which perforate the anterior 



