n8 THE SUPERIOR EXTREMITY 



also be dissected out. As a rule, a transverse anastomosing 

 twig passes between that vessel and the posterior terminal part 

 of the profunda brachii artery. It lies upon the posterior aspect 

 of the humerus, immediately proximal to the elbow-joint, and 

 can be exposed by dividing the triceps muscle a short distance 

 proximal to 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 subanconceus muscle, should be examined. Lastly, raise 

 the distal 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 anterior part of the proximal aspect of the 

 olecranon. Then revise the medial and lateral intermuscular 

 septa which are now fully exposed. 



The Medial and Lateral Intermuscular Septa. The 



medial intermuscular septum is the stronger ; it separates the 

 medial part of the medial head of the triceps from the 

 brachialis, gives attachment to both the muscles, and extends, 

 as a strong membrane, from the medial epicondyle to the in- 

 sertion of the coraco-brachialis. Then it becomes less distinct, 

 but it can be traced proximally to the lower part of the medial 

 lip of the intertubercular sulcus. At the level of the in- 

 sertion of the coraco-brachialis it is pierced by the ulnar nerve 

 and the superior ulnar collateral artery, which descend posterior 

 to it to the medial epicondyle. A short distance above the 

 medial epicondyle it is pierced by the posterior branch of 

 the inferior ulnar collateral artery. 



The lateral intermuscular septum is weaker than the 

 medial. It extends from the lateral epicondyle to the in- 

 sertion of the deltoid muscle, with which it blends, and it 

 separates the lateral part of the medial head of the triceps, 

 which is attached to its posterior surface, from the upper 

 lateral part of the brachialis, the brachio-radialis and the 

 extensor carpi radialis longus which spring from its anterior 

 surface. At the junction of the middle and distal thirds 

 of the arm it is pierced by the radial nerve and the anterior 

 branch of the profunda artery, which afterwards descend 

 along its anterior aspect, between the brachialis medially and 

 the brachio-radialis and the extensor carpi radialis longus 

 laterally. 



