THE BRACHIAL PLEXUS. 



843 



Suprascapular. 



Circumflex, 



nerve, and is afterward joined by the posterior division of the trunk, formed by 

 the junction of the eighth cervical and first dorsal nerves. It receives filaments 

 from the sixth, seventh, and eighth cervical and first dorsal nerves. At its com- 

 mencement it is placed behind the axillary and upper part of the brachial arteries, 

 passing down in front of the 

 tendons of the Latissimus dorsi 

 and Teres major. It winds 

 round the humerus in the mus- 

 culo-spiral groove with the su- 

 perior profunda artery, passing 

 from the inner to the outer side 

 of the bone, between the inter- 

 nal and external heads of the 

 Triceps muscle. It pierces the 

 external intermuscular septum, 

 and descends between the 

 Brachialis anticus and Supi- 

 nator longus to the front of 

 the external condyle, where it 

 divides into the radial and 

 posterior interosseous nerves. 



The branches of the mus- 

 culo-spiral nerve are 

 Muscular. 

 Cutaneous. 

 Radial. 

 Posterior interosseous. 



The muscular brandies are 

 divided into internal, posterior, 

 and external ; they supply the 

 Triceps. Anconeus, Supinator 

 longus, Extensor carpi radialis 

 longior, and Brachialis anti- 

 cus. These branches are de- 

 rived from the nerve at the 

 inner side, back part, and 

 outer side of the arm. 



The internal muscular 

 branches supply the inner and 

 middle heads of the Triceps 

 muscle. That to the inner 

 head of the Triceps is a long, 

 slender filament which lies 

 close to the ulnar nerve, as far 

 as the lower third of the arm. 

 and is often intimately con- 

 nected with it (ulnar collateral 

 branch). 



The posterior muscular 

 branch, of large size, arises 

 from the nerve in the groove 

 between the Triceps and the 

 humerus. It divides into branches which supply the outer and inner head of the 

 Triceps and Anconeus muscles. The branch for the latter muscle is a long, slen- 

 der filament which descends in the substance of the Triceps to the Anconeus. 



The external muscular branches supply the Supinator longus, Extensor carpi- 

 radial is longior, and (usually) the outer part of the Brachialis anticus. 



FIG. 501. The suprascapular, circumflex, and musculo-spiral 



nerves. 



