MEDIAN NERVE 701 



interval between the internal and middle flexors of the carpus. The division may occur about the 

 middle of the region, but commonly takes place in the distal third or fourth. 



The collateral In-anches arc as follows: 



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

 that name. It is gWvn off about the middle of the arm, passes beneath the lower 

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

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

 mastoido-himieralis and the biceps and divides 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 utf just as the nerve passes under the first named muscle. 



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

 and is distri])uted chiefly to the periosteum, 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 (N. volaris medialis) arises as the inner 

 t(>rminal liranch of the median nerve at a varial^le 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 beliincl the vein, the artery here becoming deeper in position. In 

 addition to cutan(H)US twigs, tlie nerve gives off about the middle of the metacar- 

 pus a consideral)le anastomotic branch which winds ol^liquely 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 

 l)ranches. 



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

 between 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 behind 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 branch. 



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

 union of the external terminal branch of the median with the deep branch of the 

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

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

 metacarpus it descends along the outer Iwrder 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 nerve, 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 diseased conditions however, 

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

 section of the volar branches only. 



' In veterinarv works these are frequently termed plantar nerves, which is an unfortunate 

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

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



