DORSUM OF THE ARM 117 



pierced the lateral intermuscular septum. One of the 

 branches to the medial head of the triceps is a long slender 

 nerve, termed the ulnar collateral nerve, on account of its 

 association with the ulnar nerve in the arm. The branch to 

 the anconaeus is a long slender twig which passes through 

 the substance of the medial head of the triceps on its way 

 to the anconaeus (Fig. 49). 



The terminal branches are the superficial ramus, which 

 is a purely cutaneous nerve, and the deep ramus, which is 

 continued into the dorsal part of the forearm as the dorsal 

 interosseous nerve, and is distributed to the muscles on 

 the dorsal aspect of the forearm, and to the radio-carpal 

 joint. These nerves will be followed later. 



Arteria Profunda Brachii. The profunda brachii artery 

 has been already seen taking origin from the brachial trunk, 

 about 25 mm. distal to the lower margin of the teres major 

 muscle. It accompanies the radial nerve, and its relations 

 to the three heads of the triceps and the sulcus for the 

 radial nerve are exactly the same as those of the nerve. 

 Before it reaches the lateral intermuscular 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 artery. 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 profunda brachii 

 artery are distributed chiefly to the three heads of the triceps 

 muscle. One twig runs proximally between the long and 

 lateral heads of the muscle, and anastomoses with the posterior 

 circumflex artery of the humerus. In that way a link is 

 established between the axillary and brachial systems of 

 branches. 



Dissection. The ulnar nerve, with the superior ulnar col- 

 lateral artery, and the slender ulnar collateral nerve, can now 

 be satisfactorily followed, as they proceed distally upon the 

 posterior aspect of the medial intermuscular 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 



