156 THE SURGICAL ANATOMY OF THE HORSE 



vein. It subsequently passes across the inner aspect of the elbow joint 

 by accompanying the main continuation of the brachial artery, namely, 

 the posterior radial, together with the vein of the same name, being 

 closely related to the internal lateral ligament of the elbow joint. In 

 the undissected limb the three structures named are here covered by the 

 posterior superficial pectoral muscle. 



Passing across the angle formed by the humerus and radius, the 

 nerve, together with the artery and vein, curves round the inner edge 

 of the latter bone, which is smoothly grooved for their accommodation, 

 and disappears by dipping between the bone and the flexor metacarpi 

 internus muscle. Passing down the forearm, it inclines slightly towards 

 the middle of the posterior surface of the radius. 



At a point which varies in the forearm, but which is usually above 

 the lower third, the nerve divides into two branches, one of which joins 

 the ulnar to form the external plantar nerve in the manner already 

 described, whilst the other is directly continued as the internal plantar 

 nerve. 



The branches of the median nerve are as follows : 



1. Twigs are distributed to the pectoral muscles before the two 

 roots unite. 



2. The Nerve to the Biceps and Coraco-humeralh Muscles. — This 

 nerve is given off in the axilla. It may come from the anterior 

 root before this unites with the posterior, or it may arise imme- 

 diately below the point of union. It passes at first downwards 

 across the inner aspect of the shoulder joint in front of the 

 axillary artery. It then passes outwards across the front of the 

 humerus, slightly superior to the prehumeral artery. Passing 

 between the two insertions of the coraco-humeralis muscle, to 

 which it distributes a number of filaments, the nerve then divides 

 into a number of branches, some of which take an upward direction 

 whilst others descend, both sets terminating in the substance of 

 the biceps muscle. 



