THE BRACHIAL PLEXUS 141 



ator (brevis] and is thereafter termed the Dorsal Interosseous 

 Nerve. It winds round the proximal part of the radius and 

 gains the posterior compartment of the forearm. It supplies 

 all;the extensor muscles of the ringers and wrist, except the 

 extensor carpi radialis longus. 



When the dorsal aspect of the forearm is examined, a dis- 

 tinct longitudinal groove is seen slightly to the ulnar side 

 of the middle line. When this groove is palpated, it is found 

 to correspond to the subcutaneous dorsal border of the ulna. 

 The extensor muscles lie to the radial side of the groove, and 

 the mass which lies to its ulnar side is formed by the flexor 

 digitorum profundus and the flexor carpi ulnaris. 



The group of muscles supplied by the dorsal interosseous 

 nerve includes the extensor carpi radialis brevis ', the extensor 

 carpi ulnaris, the extensor digitorum communis^ the extensor 

 digiti quinti proprius, the extensor indicis proprius, the abductor 

 pollicis longus, the extensor pollicis longus and brevis. 



The Superficial Branch of the Radial Nerve (O.T. Radial) 

 is purely sensory. It supplies branches to the skin (i) of the 

 thenar eminence, (2) of the radial part of the dorsum of the hand, 

 (3) of the dorsal aspects of the lateral three and a half digits, 

 except over the distal and part of the middle phalanx. It 

 must be remembered that this nerve establishes connexions 

 with (i) the lateral cutaneous nerve of the forearm (p. 134), 

 (2) the dorsal cutaneous nerve of the forearm (p. 138) 

 and (3) the dorsal branch of the ulnar nerve. On this 

 account, division of the superficial branch of the radial nerve 

 produces no appreciable alteration in the sensibility of the skin 

 areas which it supplies (Sherren). 



RADIAL (MUSCULO-SPIRAL) PARALYSIS. Complete division 

 of the radial nerve before any of its branches are given off results 

 in widespread motor paralysis, but the sensory loss is relatively 

 insignificant. The triceps and anconaeus are paralysed, and, 

 therefore, active extension of the elbow is impossible and the 

 joint is maintained in a semi-flexed attitude by the tonus of 

 the flexors of the forearm. The paralysis of the brachio- 



