MEDIAN NERVE 819 
Passing beneath the medial flexor of the carpus, the nerve continues down- 
ward in the forearm with the median vessels, and divides at a variable distance 
above the carpus into two branches; these are the medial volar nerve, and the 
lateral branch, which unites with the ulnar to form the corresponding lateral volar 
nerve. 
At the proximal part of the forearm the nerve runs almost straight downward along the 
posterior border of the long medial ligament, while the artery here inclines somewhat backward. 
Thus the nerve is superficial to the artery for a short distance, then lies in front of the latter to 
about the middle of the region, where it inclines a little backward and arrives at the interval 
between the radial and ulnar flexors of the carpus. The division may occur about the middle of 
the region or even higher, but commonly takes place in the distal third or fourth. 
The collateral branches are as follows: 
1. The musculo-cutaneous branch is in reality the continuation of the nerve of 
that name. It is given off about the middle of the arm, passes beneath 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 
brachiocephalicus 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 medial face of the forearm, carpus, and metacarpus. 
2. Muscular branches to the radial flexor of the carpus and the humeral head 
of the deep flexor of the digit are given off just as the nerve passes under the first 
named muscle. 
3. The small interosseous nerve passes through the interosseous space and 
is distributed chiefly to the periosteum, but in some cases twigs may go to the 
extensor muscles. 
The volar or metacarpal nerves,! medial and lateral, are the continuations 
of the median and ulnar nerves in the distal part of the limb. 
The medial volar nerve (N. volaris medialis) arises as the medial terminal 
branch of the median nerve at a variable distance above the carpus (Fig. 567). 
It descends through the carpal canal along the medial border of the superficial 
flexor tendon, and lies at first in front of the common digital artery. It then passes 
behind the artery to the distal third of the metacarpus, where it lies behind the vein, 
the artery here becoming deeper in position. In addition to cutaneous twigs, the 
nerve gives off near the middle of the metacarpus a considerable anastomotic 
branch which winds obliquely over the flexor tendons and joins the lateral nerve 
below the middle of the metacarpus (Fig. 572). Near the fetlock the nerve divides 
into two digital branches. 
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 corium of the hoof on the dorsal face of the digit. 
2. The volar (or posterior) digital branch (Ramus volaris) is the direct con- 
tinuation 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 volar branch, which cross very obliquely 
over the artery and anastomose in a variable manner with each other and with the 
dorsal branch. 
The lateral volar nerve (N. volaris lateralis) is formed by the union of the 
lateral terminal branch of the median with the deep branch of the ulnar nerve 
(Fig. 567). It descends with the lateral volar metacarpal artery in the texture of 
the posterior annular ligament of the carpus. In the metacarpus it descends along 
the lateral border of the deep flexor tendon behind the lateral metacarpal vein, and 
is accompanied by a small artery from the volar subecarpal arch. Toward the 
_ 1 In veterinary works these are frequently termed plantar nerves, which is an unfortunate 
misnomer. 
