38 THE SUPERIOR EXTREMITY 



Ulnar from the Medial Cutaneous Nerve of the Forearm 

 (Internal Cutaneous). They both arise from the medial cord 

 and are hidden at their origin by the axillary vein. The medial 

 cutaneous is the more anterior and the smaller of the two. 



The Radial (Musculo-spiral) is the direct continuation of 

 the posterior cord and consequently lies behind the artery. 

 It can be distinguished from the ulnar by its greater size and 

 by its position. 



REGION OF'(UPPER) ARM. 



Muscular Landmarks. The elevation produced by the 

 biceps on the front of the arm is limited by the lateral and 

 medial bicipital furrows. In its proximal part the medial furrow 

 is obscured by the coraco-brachialis } which is seen best when 

 resistance is offered to adduction of the abducted arm. 



When the elbow is forcibly extended against resistance, the 

 lateral head of the triceps gives rise to a distinct prominence, 

 which lies below and parallel to the posterior border of the 

 deltoid. The long head of the triceps can be seen, as it emerges 

 from under cover of the proximal part of the posterior border 

 of the deltoid, when the abducted arm is viewed from behind. 

 The muscular mass on the medial aspect of the back of the 

 arm is produced by the large medial head of the triceps. 



The Deep Fascia of the Arm receives attachments to the 

 humeral epicondyles and the subcutaneous border of the 

 olecranon in the elbow region. The Medial and Lateral 

 Intermuscular Septa are processes of fascia which extend from 

 the ensheathing layer to the epicondylic ridges and shaft of the 

 humerus. The medial septum extends from the medial 

 epicondyle to the insertion of the coraco-brachialis, the lateral 

 from the lateral epicondyle to the insertion of the deltoid. These 

 septa, together with the humerus, divide the arm into an anterior 

 and a posterior compartment, and, to a certain extent, limit 

 the course of pus or hsemorrhagic extravasation. 



The Triceps Brachii occupies the whole of the posterior 

 compartment of the arm, and is inserted into the proximal 

 surface of the olecranon. It is a powerful extensor of the elbow, 

 and it is supplied by the radial (musculo - spiral) nerve (C. 7 

 and 8). 



