816 
NERVOUS SYSTEM OF THE HORSE 
AXILLARY NERVE 
The axillary nerve (Figs. 566, 652)! derives its fibers chiefly from the eighth 
cervical root of the brachial plexus. 
Fic. 652.—CuTraANEOUS 
NERVES OF RIGHT 
ForetiMB OF HORSE; 
LaTeRAL Facer. 
a, Cutaneous branch 
of axillary nerve; 6, cu- 
taneous branches of radial 
nerve; c, posterior cutane- 
ous branch of ulnar nerve; 
d, cutaneous branch of me- 
dian nerve; e, superficial 
branch of ulnar nerve; f, 
lateral volar nerve; g, anas- 
tomotic branch connecting 
medial and lateral volar 
nerves; J, lateral head of 
extensor carpi 
triceps: 2, 
radialis; 3, common ex- 
tensor; 4, ulnaris lateralis. 
(After Ellenberger, in Leis- 
ering’s Atlas.) 
It runs downward and backward across 
the distal part of the subscapularis, and, in company 
with the posterior circumflex artery, dips in between that 
muscle and the subscapular artery at the level of the 
shoulder joint. Continuing outward in the interval between 
the teres minor and the long and lateral heads of the triceps, 
it reaches the deep face of the deltoid and divides into several 
divergent branches. The muscular branches supply the teres 
major, capsularis, teres minor, deltoid, and brachiocephali- 
cus. The cutaneous branch (N. cutaneus brachii lateralis) 
runs downward and a little forward across the lateral head 
of the triceps and ramifies on the fascia on the front of the 
forearm and on the superficial pectoral muscle. 
RADIAL NERVE 
The radial nerve? (Figs. 566, 568, 652) is sometimes the 
largest branch of the brachial plexus. Its fibers are derived 
chiefly from the first thoracic root of the plexus. It passes 
downward and backward over the medial surface of the origin 
of the subscapular artery and the distal part of the teres 
major. In this part of its course it is related in front to the 
ulnar nerve, which separates it from the brachial vein.’ It 
detaches a branch to the tensor fasciz antibrachii, passes out- 
ward in the interval between the teres major and the long 
and medial heads of the triceps, and gains the musculo-spiral 
groove of the humerus. Accompanied by a branch of the 
deep brachial artery, it runs obliquely downward and outward 
in the groove, covered laterally by the lateral head of the tri- 
ceps and the extensor carpi radialis, and reaches the flexion 
surface of the elbow joint. In this part of its course it gives 
off muscular branches to the three heads of the triceps and 
to the anconeus, and a cutaneous nerve (N. cutaneus anti- 
brachti dorsalis); branches of the latter emerge below or 
through the lateral head of the triceps and ramify on the 
dorso-lateral surface of the forearm. At the elbow the nerve 
descends with the anterior radial vessels on the joint capsule, 
between the brachialis and extensor carpi radialis, and sup- 
plies branches to the extensor carpi and the common extensor 
of the digit and (inconstantly) to the brachialis. Below the 
elbow joint the nerve detaches a large branch which passes 
back between the lateral extensor and the radius to the ulnaris 
lateralis, and terminates by small branches which descend on 
the radius to enter the radial and ulnar heads of the common 
and lateral extensors of the digit, and the oblique extensor of 
the carpus. Thus the radial nerve innervates the extensors 
of the elbow, carpal, and digital joints, and supplies also 
the lateral flexor of the carpus.* 
1 Also termed the circumflex nerve. 
* This is also known as the musculo-spiral nerve. 
5’ The relative positions of the vessels and nerves here are variable; not rarely the ulnar nerve 
passes between the subscapular artery and vein. 
* Morphologically the last-named muscle belongs to the extensor group. 
In man and in 
many animals it is an extensor in function. 
