MEDIAN NERVE 701 



interval hot ween the internal and middle flexors of the carpus. The division may occur about tlie 

 middle of the region, but commonl}- takes place in the distal third or fourth. 



The collateral hranclics arc as follow.s: 



1. The musculo-cutaneous branch is in reality the eontinuation of the nerve of 

 that name. It is given off about the middle of the arm, passes ])eneath the lower 

 part of the biceps, and divides into muscular and cutaneous branches. The mus- 

 cular branch enters the brachialis. The cutaneous branch emerges between the 

 mastoido-humeralis and the biceps and dividers into two branches; these descend 

 on the fascia of the forearm with the cephalic vein and its accessory, and ramify 

 on the front and inner face of the forearm, carpus, and metacarpus. 



2. Muscular branches to the internal flexor of the carpus and the flexors of 

 the digit are given off just as the nerve passes under the first named muscle. 



3. The very small interosseous nerve passes through the interosseous space 

 and is distributed chiefly to the periosteinn, but in some cases twigs may go to the 

 extensor muscles. 



The metacarpal or volar nerves/ internal and external, are the continuations 

 of the median and ulnar nerves in the distal part of the limb. 



The internal metacarpal or volar nerve (X. volaris medialis) arises as the inner 

 terminal branch of the median nerve at a variable distance above the carpus (Fig. 

 442). It descends through the carpal canal along the inner border of the super- 

 ficial flexor tendon, and lies at first in front of the large metacarpal or common 

 digital artery. It then passes behind the artery to the distal third of the metacar- 

 pus, where it lies beliind the vein, the artery here becoming deeper in position. In 

 addition to cutaneous twigs, the nerve gives off about the middle of the metacar- 

 pus a considerable anastomotic branch which winds obliquely downward and 

 outward over the flexor tendons and joins the external nerve at the lower third 

 of the metacarpus (Fig. 447). Near the fetlock the nerve divides into two digital 

 branches. 



1. The dorsal or anterior digital branch (Ramus dorsalis) descends at first 

 l^etween the digital artery and vein, then crosses over the vein and ramifies in the 

 skin and the matrix of the hoof on the dorsal (anterior) face of the digit. 



2. The volar or posterior digital branch (Ramus volaris) is the direct continua- 

 tion of the trunk. It descends Ix'hind the digital artery, which it accompanies in 

 its ramification. A middle digital branch is sometimes described as descending 

 behind the vein. In some cases this branch is distinct, but usually there are instead 

 several small twigs derived from the posterior branch, which cross very obliquely 

 over the artery and anastomose in a variable manner with each other and with the 

 anterior l)ranch. 



The external metacarpal or volar nerve (X. volaris lateralis) is formed by the 

 union of the external t(>rminal branch of the median with the deep l^ranch of the 

 ulnar nerve (Fig. 442). It descends with tlie internal volar or small metacarpal 

 artery in the texture of the posterior anntilar ligament of the carpus. In the 

 metacarptis it descends along the outer border of the deep flexor tendon behind 

 the external metacarpal vein, and is accompanied by a small artery from the volar 

 subcarpal arch. Toward the distal end of the metacarpus it is joined by the 

 oblique branch from the internal ner^•e, and beyond this is arranged like the lat- 

 ter. Below the carpus it detaches a deep branch to the suspensory ligament and 

 the interossei, and also supplies twigs to the skin. 



Anastomoses are established between the digital branches, and the areas innervated by them 

 are not well defined, but really overlap each other. In certain diseasetl conditions, however, 

 in whicli the lesions are confined to the volar structures, relief from pain may be afforded by 

 section of the volar branches only. 



' In veterinary works tliese are frecjtiently termed ])lantar nerves, wliicli is an unfortimate 

 misnomer. The writer inclines to the use of the old term metacarpal or common digital to desig- 

 nate the nerves as far as their divisions, and the term digital beyond this. 



