152 THE SURGICAL ANATOMY OF THE HORSE 



It now passes beneath the ulnar head of the middle flexor of the 

 metacarpus, and descends the back of the forearm to the carpus in a 

 manner which is almost vertical, by following closely the course of the 

 tendon of the ulnar accessorius muscle. It is next found deeply placed 

 between the tendons of the external and middle flexors of the meta- 

 carpus, just above the edge of the pisiform bone. Here the nerve 

 terminates by splitting up into two divisions. 



During its course the ulnar nerve gives off two bundles of collateral 

 branches. One of these comes off from the parent nerve about the 

 middle of the humerus, where the ulnar nerve lies on the small head of 

 the triceps. This division takes a course downwards and backwards, 

 passing between the scapulo-ulnaris and the posterior superficial pec- 

 toral muscle. It gives off a few filaments to the last mentioned muscle, 

 which it pierces to become subcutaneous, and is ultimately distributed 

 to the skin covering the inner aspect of the forearm. The other 

 branches are given off just above the condyle of the humerus, and these 

 are distributed to the anterior and ulnar heads of the flexor metacarpi 

 medius, the flexor perforatus, and the ulnar accessorius [i.e., ulnar head 

 of flexor perforans). 



One of the two terminal divisions passes across the interval between 

 the tendons of insertion of the flexor metacarpi externus and the flexor 

 metacarpi medius muscles, and becomes placed on the superficial aspect 

 of the aponeurotic covering of the forearm. It gives off a number of 

 cutaneous branches to the skin covering the outer aspect and the outer 

 part of the posterior aspect of the forearm, and ultimately splits into several 

 smaller branches which ramify superficially on the front and outer aspect 

 of the knee, and some of which may extend to the skin covering the 

 external aspect of the metacarpal region. 



The other terminal division joins one of the terminal divisions of 

 the median nerve. The latter appears in the space between the tendons 

 of the middle and internal flexors of the metacarpus, in company with 

 the posterior radial artery. It takes a course downwards on the inner 



