88 THE UPPER EXTREMITY 



those of the nerve. Before it reaches the lateral inter- 

 muscular septum, it ends by dividing into two terminal branches 

 an anterior and a posterior. The anterior and smaller branch 

 accompanies the radial nerve through the septum, and follows 

 it distally to the anterior aspect of the lateral epicondyle of 

 the humerus, where it anastomoses with the radial recurrent 

 arteries. The posterior larger branch descends on the posterior 

 surface of the lateral intermuscular septum, and anastomoses 

 on the back of the lateral epicondyle of the humerus with 

 the interosseous recurrent artery. 



The branches which proceed from the art. profunda brachii 

 are chiefly distributed to the three heads of the triceps 

 muscle. One twig ascends between the long and lateral 

 heads of the muscle, and anastomoses with the posterior 

 circumflex artery of the humerus. In this way, a link is 

 established between the axillary and brachial systems of 

 branches. 



Dissection. The ulnar nerve, with the superior ulnar collateral artery, 

 and the slender ulnar collateral nerve, can now be advantageously followed, 

 as they proceed distally upon the posterior aspect of the medial inter- 

 muscular septum. They are covered by a thin layer of fleshy fibres 

 belonging to the medial head of the triceps. The posterior branch of 

 the inferior ulnar collateral artery, after it has pierced the medial septum, 

 should also be dissected out. As a rule, a transverse branch passes 

 between this vessel and the posterior terminal part of the a. profunda 

 brachii. It lies upon the posterior aspect of the humerus, immediately 

 above the elbow-joint, and can be exposed by dividing the triceps muscle 

 a short distance above the olecranon. At the same time the fleshy fibres 

 of the medial head of the triceps, which are inserted into the posterior 

 part of the capsule of the elbow-joint, and constitute the subanconaus 

 muscle, should be examined. Lastly, raise the lower piece of the triceps 

 from the elbow-joint, and look for a small bursa mucosa between the deep 

 surface of the triceps tendon and the upper aspect of the olecranon. 



ARTICULATIO HUMERI (SHOULDER-JOINT). 



Before proceeding to the dissection of the forearm it 

 is advisable to study the articulatio humeri (shoulder-joint), 

 because if this is deferred too long the ligaments are apt to 

 become dry. 



In no joint in the body is the movement so free, and so varied in its 

 character, as in the shoulder-joint. This is rendered necessary by the 

 many functions which are performed by the upper limb. Freedom of 

 motion is provided for in two ways (i) by the large size of the head of 

 the humerus, in comparison with the small dimensions and shallow character 



