THE BRACHIAL PLEXUS 145 



bone. Under ordinary conditions, the muscle acts along with the other 

 flexors of the wrist, but, when it contracts alone, it produces ulnar de- 

 viation of the hand in addition to flexion of the wrist. Ulnar deviation of 

 the hand, without either flexion or extension, is produced by the simul- 

 taneous contraction of the flexor carpi ulnaris and the extensor carpi 

 ulnaris. Inability to carry out this movement must indicate paralysis or 

 parsesis of one or other of these muscles. 



In the distal part of the forearm the ulnar nerve gives 

 off a volar (palmar) cutaneous branch, which supplies the skin 

 over the hypothenar eminence, and a dorsal cutaneous branch, 

 which supplies the ulnar side of the dorsum of the hand and 

 the proximal parts of the dorsal aspects of the little ringer and 

 the ulnar side of the ring ringer. 



In the hand, the ulnar nerve terminates by dividing into 

 superficial and deep branches. The superficial branch 

 supplies the skin on the volar aspect of the little finger and 

 the ulnar side of the ring finger. In addition, it supplies 

 the distal parts of the dorsal aspects of the same two digits. 



The Deep Branch of the Ulnar Nerve gives off no cutaneous 

 branches, but it supplies the muscles of the hypothenar 

 eminence, all the interossei, the medial two lumbricals and the 

 adductor pollicis. 



The muscles which constitute the hypothenar eminence com- 

 prise the abductor, the opponens and the flexor brevis digiti 

 quinti. The actions of these muscles are indicated by their 

 names, but, under normal conditions, the little finger possesses 

 little power of opposition, as the ligaments of the joint between 

 the fifth metacarpal bone and the hamate (unciform) bone allow 

 very little rotatory movement. 



Atrophy of this group of muscles is easily recognised. It 

 occurs in lesions (i) of the ulnar nerve, (2) of the lower trunk 

 of the brachial plexus, e.g. Klumpke's paralysis, or following 

 pressure by a cervical rib, and (3) of the lower part of the 

 cervical enlargement of the spinal medulla, e.g. progressive 

 muscular atrophy. 



The Lumbricals are four small muscles which arise from the 

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