838 THE NERVOUS SYSTEM, 



From the inner cord arise the internal of the two anterior thoracic nerves, the 

 internal cutaneous, the lesser internal cutaneous (nerve of Wrisberg), the ulnar, and 

 inner head of the median. 



From the posterior cord arise two of the three subscapular nerves, the third 

 arising from the posterior division of the trunk formed by the fifth and sixth 

 cervical nerves ; the cord then divides into the musculo-spiral and circumflex 

 nerves. 



These may be arranged according to the parts they supply : 



To the chest .... Anterior thoracic. 



To the shoulder . { Subscapular. 



( Circumflex. 

 Musculo-cutaneous. 

 Internal cutaneous. 



m ,1 c i Lesser internal cutaneous. 



To the arm, forearm, and hand . ^ M d' 



Ulnar. ' 

 ^ Musculo-spiral. 



The fasciculi of which these nerves are composed may be traced through the 

 plexus to the spinal nerves from which they originate. They are as follows : 



External anterior thoracic from 5th, 6th, and 7th cervical. 



Internal anterior thoracic " 8th cervical and 1st dorsal. 



Subscapular " 5th, 6th, 7th, and 8th cervical. 



Circumflex " 5th, 6th, 7th, and 8th cervical. 



Musculo-cutaneous " 5th, 6th, and 7th cervical. 



Internal cutaneous " 8th cervical and 1st dorsal. 



Lesser internal cutaneous " 1st dorsal. 



Median " 6th, 7th, and 8th cervical, and 1st dorsal. 



Ulnar " 8th cervical and 1st dorsal. 



Musculo-spiral " 6th, 7th, and 8th cervical, and 1st dorsal. 



The Anterior Thoracic Nerves (Fig. 500), two in number, supply the Pectoral 

 muscles. 



The external or superficial nerve, the larger of the two, arises from the outer 

 cord of the brachial plexus, through which its fibres may be traced to the fifth, 

 sixth, and seventh cervical nerves. It passes inward, across the axillary artery 

 and vein, pierces the costo-coracoid membrane, and is distributed to the under 

 surface of the Pectoralis major. It sends down a communicating filament to join 

 the internal nerve, which forms a loop round the inner side of the axillary 

 artery. 



The internal or deep nerve arises from the inner cord, and through it from 

 the eighth cervical and first dorsal. It passes upward between the axillary artery 

 and vein, and joins with the filament from the superficial nerve. It then passes 

 to the under surface of the Pectoralis minor muscle, where it divides into a number 

 of branches, which supply the muscle on its under surface. Some of the branches 

 pass through the muscle ; others wind round its upper border and pierce the costo- 

 coracoid membrane to supply the Pectoralis major. 



The Subscapular Nerves, three in number, supply the Subscapularis, Teres 

 major, and Latissimus dorsi muscles. The fasciculi of which they are composed 

 may be traced to the fifth, sixth, seventh, and eighth cervical nerves. 



The upper subscapular nerve, the smallest, enters the upper part of the Sub- 

 scapularis muscle. 



The lower subscapular nerve enters the axillary border of the Subscapularis 

 and terminates in the Teres major. The latter muscle is sometimes supplied by a 

 separate branch. 



The middle or long subscapular, the largest of the three, follows the course of 



