THE BRACHIAL PLEXUS. 769 



These may be arranged according to the parts they supply : 



To the chest '. .* . . Anterior thoracic. 



To the shoulder . / Subscapular. 



( Circumflex. 

 ( Musculo-cutaneous. 

 Internal cutaneous. 



To the arm, forearm, and hand . \ \f s ]. er internal cuta neous. 



I Median. 



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 and 6th cervical. 



Musculo-cutaneous " 5th and 6th 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, sometimes also 



from the 5th. 



The Anterior Thoracic Nerves (Fig. 413), 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 behind the first part of the axillary 

 artery, then curves forward between the axillary artery and vein, and joins with 

 the filament from the anterior 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 two or three branches pass through the 

 muscle 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 ; this nerve is frequently represented by two branches. 



The loiver subsaapular 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 

 the subscapular artery, along the posterior wall of the axilla to the Latissimus 

 dorsi, through which it may be traced as far as its lower border. 



The Circumflex Nerve (Fig. 414) supplies some of the muscles and the integu- 

 ment of the shoulder and the shoulder-joint. It arises from the posterior cord of 

 the brachial plexus, in common with the musculo-spiral nerve, and its fibres may 

 be traced through the posterior cord to the fifth and sixth cervical nerves. It is 

 at first placed behind the axillary artery, between it and the Subscapularis muscle, 

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