102 THE SUPERIOR EXTREMITY 



wrist, but if no other nerves are involved, no sensory change is 

 apparent (vide infra). 



Injury to the Radial (Musculo-Spiral) nerve occurs most 

 commonly in its distal third beyond the origin of its cutaneous 

 branches and of the nerve-supply of the triceps and the anconseus. 

 All the remaining muscles supplied directly by the radial 

 (musculo-spiral) nerve (p. 73) and indirectly by its deep branch 

 (posterior interosseous nerve) are paralysed, and the characteristic 

 deformity of " Drop Wrist " develops. The patient is unable 

 to extend his wrist or fingers, but, if the first phalanges are 

 supported when he attempts to do so, the lumbricals and interossei, 

 which act in harmony with the extensor apparatus, will extend 

 the fingers at the inter -phalangeal joints (p. 84). 



No sensory changes accompany injury to the radial (musculo- 

 spiral) nerve in its distal third. Its superficial branch (radial 

 nerve) is paralysed, but on account of the communications 

 which it establishes with other nerves, no change of sensibility 

 can be determined. 



Note. The dorsal branch of the lateral cutaneous (from the musculo- 

 cutaneous nerve), the superficial (radial) branch of the radial (musculo- 

 spiral) nerve, and the dorsal cutaneous nerve of the forearm (lower external 

 cutaneous branch of the musculo-spiral) communicate with one another 

 and overlap to such an extent that no sensory symptoms are produced by 

 section oj any one of the nerves by itself. If any two are injured there is some 

 loss of epicritic and protopathic sensibility, extending from the bases of the 

 lateral three digits to the dorsum of the wrist, but complete epicritic and 

 protopathic loss in this area occurs only after division of all three (Sherren). 



When the dorsal interosseous nerve is injured, the motor 

 symptoms are the same as those described above, except that 

 the brachio-radialis and extensor carpi radialis longus escape. 

 As a result, the patient is able to extend the wrist, but the 

 movement is weak. 



The " Drop Wrist " of lead poisoning can be differentiated 

 from both the above varieties, as the brachio-radialis is not 

 affected while the extensor carpi radialis longus is paralysed. 



Musculo-Cutaneous Nerve. The main trunk of this nerve 

 is rarely injured by itself, but the cutaneous portion or one of 

 its branches may be cut in incisions and wounds of the forearm. 



In injury of the main trunk, the biceps and the coraco- 

 brachialis are paralysed and the brachialis is weakened (p. 41). 

 Flexion of the forearm is still possible, and is performed by the 

 krachialis and the superficial flexors of the forearm when the 

 hand is supine, but, when the forearm is in the prone or mid- 



