io 4 THE SUPERIOR EXTREMITY 



balance is further upset by paralysis of the lumbrical muscles 

 (p. 84), and as the action of these muscles on the dorsal extensor 

 expansion (p. 92) is lost, hyper- extension at the metacarpo- 

 phalangeal joints and flexion at the inter-phalangeal joints 

 result. The thumb is abducted owing to paralysis of the 

 adductor, and consequently the grasping power of the hand is 

 greatly diminished. 



When the ulnar nerve is cut distal to the origin of its dorsal 

 cutaneous branch, epicritic sensibility is lost over the ulnar side 

 of the palm, the palmar aspects of the little ringer and ulnar side 

 of the ring ringer, and the dorsal aspects of the second and third 

 phalanges of the same fingers. Protopathic loss varies, and 

 deep sensibility is always present in these cases unless many 

 tendons are cut. When the injury occurs proximal to the origin 

 of the dorsal cutaneous branch, all the previous sensory symptoms 

 are present, and, in addition, epicritic sensibility is lost over the 

 ulnar side of the dorsum of the hand and over the dorsal aspects 

 of the proximal phalanges of the little finger and ulnar side of 

 the ring finger. 



2. At the Elbow. In injury of the ulnar nerve at this site, 

 the additional muscular paralysis produces a slight change in 

 the deformity of the hand. The portion of the flexor digitorum 

 profundus destined for the ring and little fingers is paralysed, 

 and therefore the terminal phalanges of these fingers are not 

 flexed, as in (i), but are hyper-extended by the unopposed 

 action of the extensor expansion. Radial deviation of the 

 hand occurs on flexion of the wrist owing to paralysis of the 

 flexor carpi ulnaris. 



The sensory changes are exactly similar to those which occur 

 in section of the nerve at the wrist above the origin of the dorsal 

 cutaneous branch. In addition, there is some loss of deep 

 sensibility on the ulnar side of the palm. 



Median Nerve. The median nerve is most commonly injured 

 as it lies between the tendons of the palmaris longus and the 

 flexor carpi radialis at the proximal border of the transverse 

 carpal ligament (p. 67). It is here cut by stab-wounds, the 

 neighbouring tendons usually escaping injury. 



Motor Symptoms. The abductor and the flexor pollicis 

 brevis, the opponens pollicis, and the first and second lumbricals 

 are the only muscles affected. The thumb cannot be abducted 

 (p. 84), but the movement of opposition may be imitated by 

 the flexor pollicis longus. When the patient is told to close the 



