154 THE NERVOUS SYSTEM 



exceeds the area of protopathic loss. It affects the radial 

 part of the palm, the volar aspects of the thumb, index, middle 

 and ulnar half of the ring finger, and the dorsal aspects of 

 the distal halves of the index, middle and ulnar half of the 

 ring finger. The dorsum of the thumb is never affected in 

 injuries to the median nerve. 



(I}} When the median nerve is divided in the axilla or arm, 

 all the flexor and pronator muscles are paralysed, except the 

 flexor carpi ulnaris and the ulnar half of the flexor digitorum 

 profundus. The ring and the little fingers retain their 

 lumbricals and interossei, in addition to their profundus 

 tendons, and they are therefore little affected. The middle 

 and index fingers, however, only retain their interossei, as both 

 the flexor digitorum sublimis and profundus and the first two 

 lumbricals are paralysed. They are extended or hyper- 

 extended at the metacarpo-phalangeal joints and extended at 

 the interphalangeal joints. Active flexion of these fingers 

 can only be carried out at the metacarpo-phalangeal joints, 

 and it is then produced by the interossei. 



The thumb is maintained extended and adducted. Flexion 

 of the terminal phalanx is impossible and flexion of the 

 proximal phalanx is a weak movement, produced by the un- 

 paralysed adductor pollicis. Abduction can be simulated by 

 the abductor pollicis longus, as has been described above, 

 but, owing to the paralysis of the flexor pollicis longus, 

 opposition of any kind, either true or false, is impossible. 



The forearm is held in the supine position and, as both the 

 pronator teres and quadratus are paralysed, true pronation is 

 impossible. The brachio-radialis is able to initiate the move- 

 ment (p. 140), and, if the arm is then abducted to a right 

 angle, the weight of the partially pronated hand can complete 

 the movement. 



The sensory phenomena are restricted to the same areas as 

 before (vide supra), but deep sensibility is absent over the middle 

 and index fingers, and, in many cases, over a wider area, which 

 is more or less co-extensive with the area of protopathic loss. 



