THE BRACHIAL PLEXUS. 



1313 



Fig 



Inf. ext. cutaneous 



br. of musculo-' 



spiral nerves 



Musculo-cuta- 



neous nerve, ant. 



cutaneous br. 



Musculo-cuta 



neous nerve, post 



cutaneous br. 



Lesser internal 

 cutaneous nerve 



Internal cutaneous 

 nerve 



The extensor ossis metacarpi pollicis and the extensor brevis pollicis are innervated by a 

 branch arising below tke preceding, which breaks up into two decurrent twigs, one of which 

 goes to each muscle. 



The extensor longus pollicis is the recipient of a small filament, which arises from the 

 posterior interosseous a short distance below the preceding nerve. 



The extensor indic'is is sup- 

 plied by the lowermost motor 

 filament arising from the poste- 

 rior interosseous. 



Terminal twigs are distrib- 

 uted to the dorsal portion of the 

 wrist joint, the intercarpal and 

 carpo-metacarpal joints, the peri- 

 osteum of the radius and ulna 

 and the interosseous membrane. 

 One of the filaments supplying 

 the last-mentioned structure fre- 

 quently inosculates with a branch 

 from the anterior interosseous. 



The filaments to the carpus 

 are continued through the meta- 

 carpal spaces and are joined by 

 twigs from the deep branch of 

 the ulnar (page 1305). The joint 

 nerves thus formed break up into 

 two branches which accompany 

 adjoining metacarpal bones to 

 the metacarpo-phalangeal articu- 

 lations. The branch to the first 

 metacarpal space breaks up into 

 seven branches (Rauber). 



Radial nen-e 



Brs. of ant. br. of 

 musculo-cutaneotis 



Ant. br. internal 

 cutaneous ner\'e 



From radial, 

 nerve 



Digital brs. 



of median 



nerve 





Palmar cuta- 

 — neous br. of ul- 

 nar nerve 



Palmar cutane- 

 ous br. of me- 

 dian nerve 



Digital brs. of 

 ulnar nerve 



Digital brs. of 

 median nerve 



bb. The radial nerve 

 (r, superficialis n. radialis) 

 (Fig. 1095) is smaller than 

 the posterior interosseous 

 and is purely sensory in its 

 function. Its fibres originate 

 from the sixth cervical nerve 

 and sometimes from the fifth 

 or seventh. From the end of 

 the musculo-spiral it passes 

 down the radial side of the 

 forearm under cover of the 

 brachio-radialis and anterior 

 to the supinator brevis, the 

 pronator radii teres and the 

 radial head of the flexor 

 sublimis digitorum. It 

 accompanies, for the greater 

 part of its course, the radial 

 artery, to the radial side of 

 w^hich the nerve lies. At the 

 junction of the middle and 

 lower thirds of the forearm 

 it begins to turn gradually 

 backward over the radius and under the tendon of the brachio-radialis (Fig. 1095). 

 Reaching the extensor surface of the forearm just above the wrist it divides into 

 two diverging branches, which supply the back of the hand and the three outer 

 digits (Fig. 1 102). 



Branches. — The radial nerve divides into two terminal branches, an external 

 and an internal. 



Superficial dissection of ria:ht forearm and hand, showing cutaneous 

 nerves of atiterior and palmar surface. 



