THE BRACHIAL PLEXUS 149 



When the ulnar nerve is injured distal to the origin of its 

 dorsal cutaneous branch, only the distal phalanges of the little 

 and ring fingers are affected on the dorsal aspect of the hand. 

 On the volar aspect, the loss of epicritic sensibility is the 

 same as in the former case, but protopathic loss only affects 

 the little finger. 



When the ulnar nerve is injured at or proximal to the elbow, 

 the motor symptoms which have already been described are 

 increased by the paralysis of the flexor carpi ulnaris and the 

 ulnar half of the flexor digitorum profundus. As a result, 

 flexion of the wrist is weakened and, when that movement is 

 actively performed, the hand becomes deviated to the radial 

 side. It might appear as if paralysis of the ulnar portion of 

 the flexor digitorum profundus would result in hyperextension 

 of the distal interphalangeal joints, but, as there is only one 

 extensor muscle for all the joints of the fingers, the distal 

 joints cannot be extended when the proximal interphalangeal 

 joints are flexed. The attitude of the fingers, therefore, is not 

 altered by the additional paralysis, and the characteristic 

 main en griffe is present, as in the case of injury to the 

 nerve proximal to the wrist. 



The sensory loss is very similar to that found when the 

 ulnar nerve is divided proximal to the point of origin of its 

 dorsal cutaneous branch, with the important difference that 

 deep sensibility is lost over an area, which corresponds more 

 or less accurately to the area of protopathic loss. 



The Median Nerve (C. 5, 6, 7, 8 and T. i) is formed in 

 the axilla by the union of a lateral head, derived from the 

 lateral cord, with a medial head, derived from the medial 

 cord. In the axilla and the arm, the median nerve is closely 

 related to the great vessels and it gives off no branches 

 until it supplies the superficial group of muscles of the 

 forearm. These branches arise just proximal to the elbow 

 and they are distributed to the pronator teres, the flexor 

 carpi radialis, the palmaris longus and the ^flexor digitorum 

 sublimis. 



