i 4 4 THE NERVOUS SYSTEM 



experienced in the area supplied by this nerve. In the latter 

 case, the condition may be caused by direct pressure on the 

 nerve by enlarged lymph glands in the axilla. 



The Medial Cutaneous Nerve of the Forearm (Internal 

 Cutaneous) (C. 8 and T. i) pierces the deep fascia about 

 half-way down the arm, and divides into volar (anterior) and 

 ulnar (posterior) branches. These two branches are respons- 

 ible for the supply of the skin over the medial half of the 

 forearm, and, although they overlap one another with great 

 freedom, they do not overlap the adjoining nerves to the 

 same extent. As a result, when either branch is divided 

 alone, the sensory loss is sharply demarcated on the radial 

 side, but it disappears very gradually on the ulnar side. The 

 area supplied by this nerve may be involved in the referred 

 pain of angina pectoris (p. 192). 



The Ulnar Nerve (C. 8 and T i) arises from the medial 

 cord of the plexus in the axilla, and is placed on the medial 

 side of the brachial artery in the proximal part of the arm. 

 In the distal part of the arm it leaves the anterior compart- 

 ment and passes behind the medial epicondyle of the humerus. 

 In this situation the nerve is only covered by skin and fasciae, 

 and, as it is in direct contact with the bone, it is consequently 

 exposed to injury. 



At the elbow, the ulnar nerve supplies branches to the flexor 

 carpi ulnaris and to the part of the flexor digitorum profundus 

 which acts on the ring and little fingers. 



Its course through the forearm corresponds to a line drawn 

 from the medial epicondyle to the lateral side of the pisiform 

 bone, which can easily be felt on the ulnar side of the wrist at 

 the proximal border of the hypothenar eminence. Proximally 

 it is covered by the fleshy belly of the flexor carpi ulnaris, but 

 near the wrist it becomes superficial and lies on the lateral 

 side of the tendon of that muscle. 



The Flexor Carpi Ulnaris arises both from the medial epicondyle and 

 from the medial side of the olecranon. It descends on the ulnar side of 

 the forearm, and its tendon can be traced to its insertion into the pisiform 



