THE BRACHIAL PLEXUS 105 



hand slowly, the index and middle fingers lag behind the other 

 two, as the balance between the extensors and flexors is disturbed 

 by the lumbrical paralysis (see Ulnar Nerve, p. 103). Hyper- 

 extension of the index and middle fingers at the metacarpo- 

 phalangeal joints and adduction of the thumb are the 

 characteristic features of the condition when the hand is at rest. 



Sensory Symptoms. Epicritic sensibility is lost over the 

 palm of the hand and over the area supplied by the digital 

 branches. On the dorsal aspect, epicritic sensibility is lost over 

 the second and third phalanges of the same fingers, but there is 

 no sensory change on the dorsum of the thumb. The radial 

 side of the thenar eminence is not affected. If many tendons 

 are cut, as well as the nerve, deep sensibility is interfered with, 

 and there is additional muscular paralysis. 



When the median nerve is injured proximal to the bend of 

 the elbow, the sensory symptoms are the same as those described 

 above, but, in addition, deep sensibility is diminished over the 

 palmar aspect of the hand and fingers. The amount of muscular 

 paralysis is greatly increased, as the nerve is injured proximal 

 to the origin of the branches supplying the muscles on the front 

 of the forearm (p. 72). True pronation is lost, but the brachio- 

 radialis carries the forearm from the supine into the mid-prone 

 position and then, if the arm is abducted, the weight of the 

 hand can complete the action. Flexion of the wrist with ulnar 

 deviation is performed by the flexor carpi ulnaris and the ulnar 

 half of the flexor digitorum profundus. The thumb is still 

 adducted, but the terminal phalanx is kept extended owing to 

 paralysis of the flexor pollicis longus. The index and middle 

 fingers are practically useless, as no flexion is possible at the 

 inter-phalangeal joints, and the interossei which are the only 

 flexor muscles unaffected are but feeble flexors of the metacarpo- 

 phalangeal joints when they have to initiate the movement. 

 On the other hand, the ring and' little fingers are weakened only 

 by the loss of the flexor digitorum sublimis tendons. 



Segmental Inner vation of the Muscles of the Superior 

 Extremity. The statements made in the foregoing pages 

 regarding the segmental innervation of the individual muscles 

 are substantially in agreement with the descriptions given in 

 modern anatomical text-books, but they differ, in many instances, 

 from the descriptions given by Kocher, whose views are based 

 on clinical data. His conclusions are embodied in the following 

 table : 



