DISSECTING MANUAL. 



gives off the external anterior thoracic, musculo-cutaneous, 

 and median (outer head) ; the inner gives off the ulnar, median 

 (inner head), internal cutaneous, lesser internal cutaneous, 

 and internal anterior thoracic ; the posterior cord gives off the 

 circumflex, three subscapular, and the musculo-spiral. These 

 are divided into two sets, an anterior derived from the inner 

 and outer cords, and a posterior derived from the posterior 

 cord. [625] 



Anterior Thoracic Nerves. The external arises from the 

 outer cord by three roots, from the fifth, sixth, and seventh 

 cervical; and the internal from the inner cord, from the last 

 cervical and first thoracic. Each descends on either side of the 

 axillary artery; a communicating loop crosses the artery and 

 connects them. Branches of the external pierce the costo- 

 coracoid membrane to reach the sternal and clavicular por- 

 tions of the Pectoralis major. Branches of the internal and of 

 the communicating loop pierce the Pectoralis minor, supply- 

 ing it and the sternal part of the Pectoralis major. [626] 



Musculo-cutaneous. Arising from the outer cord this de- 

 scends between the axillary artery and the Coraco-brachialis, 

 and then through the latter and betvveen the Biceps and 

 Brachialis anticus to the bend of the elbow ; here it pierces the 

 deep fascia and divides into cutaneous branches, anterior and 

 posterior, for the outer side of the forearm. Muscular branches 

 supply both heads of the Biceps, and the Brachialis anticus; 

 the nerve to the Coraco-brachialis, from the seventh cervical, 

 usually arises with it but soon separates. [627] 



Median. The outer head arises from the outer cord and 

 descends on the outer side of the axillary artery; the inner 

 head, arising from the inner cord, crosses the artery to join the 

 outer head in the upper arm. The united nerve descends on 

 the outer side of the brachial artery, then crosses this to the 

 inner side and enters the forearm between the heads of the 

 Pronator radii teres. It has no branches in the arm. [627] 



Ulnar. Arising from the inner cord, this descends between 



[162] 



