408 BRACHIAL PLEXUS BRANCHES. 



In the axilla, it is situated at first to the outer side and then behind 

 the axillary artery, resting by its outer border against the tendon 

 of the subscapularis muscle. At this point it completely surrounds 

 the artery by means of the two cords which are sent oft' to form the 

 median nerve. 



Its Branches may be arranged into two groups, humeral and de- 

 scending, 



Humeral Branches. Descending Branches. 

 Superior muscular, External cutaneous, 



Short thoracic, Internal cutaneous, 



Long thoracic, Lesser internal cutaneous, 



Suprarscapular, Median, 



Subscapular, Ulnar, 



Inferior muscular. Musculo-spiral, 



Circumflex. 



The superior Muscular nerves are several large branches which 

 are given off by the fifth cervical nerve above the clavicle ; they 

 are a subclavian branch to the subclavius muscle, which usually 

 sends a communicating filament to the phrenic nerve ; a rhomboid 

 branch to the rhomboidei muscles; and frequently an angular branch 

 to the levator anguli scapulae. 



The Short thoracic nerves are two in number ; they arise from the 

 brachial plexus at a point parallel with the clavicle, and are divisible 

 into an anterior and a posterior branch. The anterior branch passes 

 forwards between the subclavius muscle and the subclavian vein, 

 and is distributed to the pectoralis major muscle, entering it by its 

 costal surface. In its course it gives off a branch which forms a 

 loop of communication with the posterior branch. The posterior 

 branch passes forward beneath the axillary artery and unites with 

 the communicating branch of the preceding to form a loop, from 

 which numerous branches are givSn off to the pectoralis major and 

 pectoralis minor. 



The Long thoracic nerve (external respiratory of Bell) is a long 

 and remarkable branch arising from the fourth and fifth cervical 

 nerves, immediately after their escape from the intervertebral fora- 

 mina. It passes down behind the plexus and axillary vessels, resting 

 on the scalenus posticus muscle ; it then descends along the side of 

 the chest upon the serratus magnus muscle to its lowest serration. 

 It sends numerous filaments to this muscle in its course. 



The Supra-scapular nerve arises above the clavicle from the fifth 

 cervical nerve and descends obliquely outwards to the supra-scapu- 

 lar notch ; it then passes through the notch, crosses the supra-spinous 

 fossa beneath the supra-spinatus muscle, and passing in front of the 

 concave margin of the spine of the scapula enters the infra-spinous 

 fossa. It is distributed to the supra-spinatus and infra-spinatus 

 muscle. 



The Subscapular nerves are three or four in number; of which 

 one arises from the brachial plexus above the clavicle, and the 



