NERVOUS SYSTEM. ^53 



The scapular neuves may be distinguished into the ante- 

 rior, the posterior, and the subscapular nerves. 



The ai/teriur scapular nerve is reflected upward and forward, 

 in company with the artery of that name ; winds rounds tlie ante- 

 rior costa of the scapula, between the subscapularis and antea- 

 spinatus, to which njuscles it sends off branches in crossing the 

 dorsum scapulae, and stretches its ultimate filaments into the 

 triceps. 



The posterior scapular nerve, after detaching a branch to the 

 subscapularis, dips between that muscle and the triceps. There 

 the trunk splits into several branches which penetrate the triceps, 

 teres minoi-, and shoulder-joint : one of them is continued upon 

 the outside, round the cervix humeri, where it becomes subcuta- 

 neous, and ends in the insertion of the levator humeri. 



The subscapular nerves, two, three, or four in number, issue 

 from the top of the plexus, and ascend between the scapula and 

 the ribs, and enter the substance of the subscapularis. 



The spiral nerve, the largest of the nervous trunks fur- 

 nished by the axillary plexus, arises behind the humeral artery, 

 and for a short distance accompanies the vessel. It then leaves 

 the artery and turns round the back of the os humeri, between 

 the bone and the large head of the triceps, and is to be found, 

 covered by that muscle, coursing the outward surface of the body 

 of the same bone. Next, it plunges deep among the heads of 

 the extensors ; afterwards, much diminished in size, it insidiously 

 creeps round the neck of the radius, and penetrates the head of 

 the flexor metacarpi externus, among the fibres of which its re- 

 maining ramifications are expended. Its branches are — 1. Near 

 its origin, three or four long branches are sent down to the tri- 

 ceps. 2. Lower down, a branch is separated which pierces that 

 muscle and gains the front of the elbow-joint, where it escapes 

 through the faschia and takes its course under the skin covering 

 the arm, and ramifies upon the fore and outward part of the knee: 

 this nerve may be distinguished as the external cutaneous nerve. 

 3. Several considerable branches that penetrate the heads of the 

 extensor muscles. 



The radial nkrve clings to the humeral artery, with which 

 it descends to the inward side of the elbow-joint, and runs down 

 behind the vessel, along the back of the radius, to the knee ; 

 there it passes under the posterior annular ligament, and con- 

 tinues its course with the artery, and, as soon as it has descended 

 upon the leg, takes the name of the internal metacarpal nerve. 

 Its branches are — 1. Which comes ofl' the trunk a little below its 

 origin, from its size and importance is distinguished as the mus- 

 culo-cutaneous nerve. After accompanying the trunk for a short 

 z z 



