148 THE NERVOUS SYSTEM 



of the thumb, which is the reverse movement, must also occur 

 in this plane (see also p. 151). 



When the ulnar nerve is divided near the wrist, all the 

 intrinsic muscles of the hand are paralysed, with the exception 

 of those supplied by the median nerve (p. 151). Owing to the 

 paralysis of the interossei, the movements of abduction and 

 adduction of the ringers are lost, but not necessarily entirely so 

 as their actions may be simulated by the extensor digitorum 

 communis, which, however, can only act when the fingers are 

 extended. At the same time it must be remembered that, mainly 

 owing to the arrangement of the collateral ligaments of the 

 metacarpo-phalangeal joints, free abduction and adduction of the 

 fingers can only be carried out when the joints are in a position 

 of extension. Abduction of the little finger and adduction of 

 the thumb are impossible, although the latter movement may 

 be simulated by the flexor pollicis longus and brevis. 



The fingers adopt a characteristic attitude. Owing to the 

 paralysis of their interossei, the index and middle fingers are 

 extended at the metacarpo-phalangeal joints and the ring and 

 little fingers adopt a greater degree of the same attitude, as 

 their lumbrical muscles are also paralysed. Hyperextension 

 of the ring and little fingers at the metacarpo-phalangeal joints 

 stretches the tendons of the flexor digitorum sublimis and 

 profundus, which contract and flex the interphalangeal joints. 

 The degree of flexion present in the interphalangeal joints of 

 the index and middle fingers is much less, as their lumbrical 

 muscles are able to oppose the action. 



The sensory loss depends on the site of the injury. If it 

 occurs proximal to the origin of the dorsal cutaneous branch^ 

 the sensory loss involves the ulnar halves of both dorsal and 

 volar aspects of the hand, the whole of the little finger and 

 the ulnar half of the ring finger. Unless the injury which 

 divided the nerve has also divided some of the tendons, there 

 is no loss of sensibility to deep pressure. Epicritic sensibility 

 is lost over the whole of the area indicated, but the area of 

 protopathic loss is much smaller (see p. 121). 



