698 



NERVOUS SYSTEM OF THE HORSE 



several divergent branches. The muscular branches supply the teres major, cap- 

 sularis, teres minor, infraspinatus, deltoid, and nuistoido-humeralis. The cutane- 

 ous branch (N. cutaneus brachii lateralis) runs downward and a little forward 

 across the external 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. 441, 443, 520), also called 

 the musculo-spiral, is sometimes the largest branch of 

 the brachial plexus. Its fibers are derived from the 

 seventh and eighth cervical and first thoracic roots of 

 the plexus. It passes downward and backw-ard over 

 the inner surface of the subscapular artery and 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 fasciae antibrachii, 

 passes outward in the interval between the teres major and 

 the long and internal 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 down- 

 ward and outward in the groove, covered externally by the 

 external head of the triceps and the extensor carpi radialis, 

 and reaches the flexion surface of the elbow joint. In this 

 part of its course it gives off a muscular branch which 

 ramifies in the long and external heads of the triceps and in 

 the anconeus, and a cutaneous nerve (N. cutaneus anti- 

 jjrachii dorsalis); branches of the latter emerge below or 

 through the external 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 Ijrachialis and extensor carpi radialis, and sup- 

 plies branches to the extensor carpi and the common or 

 anterior extensor of the digit and (inconstantly) to the 

 brachialis. Below the elbow joint the nerve detaches a 

 large branch which passes back to the flexor carpi ex- 

 ternus, and terminates by small branches which descend 

 on the radius to enter the radial and ulnar heads of the 

 common extensor, the lateral extensor, 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 flexor carpi externus.^ 



Fig. 520. — Cutaneous 

 Nerves of Right 

 Fore Limb of 

 Horse, External 

 Face. 



a. Cutaneous branch 

 of axillary nerve; b, 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; /, 

 external metacarpal nerve; 

 (7, anastomotic branch con- 

 necting internal and exter- 

 nal metacarpal nerves; 1 , 

 external head of triceps; 2, 

 extensor carpi radialis; 3, 

 anterior extensor; 4. flexor 

 carpi externus. (After El- 

 lenberger, in Leisering's 

 Atlas.) 



Ulnar Nerve 



The ulnar nerve (Figs. 441, 442, 443, 520) arises with 



the median from the thoracic components of the brachial 



plexus. It descends between the brachial artery and 



vein, accompanied for a short distance by the radial 



nerve. It then crosses the vein and continues behind 



the latter along the anterior border of the tensor fasciae 



antibrachii and dips under that muscle near the elbow. Here it is joined 



by the ulnar vessels and passes downward and backward over the internal 



^ Morphologically the last-named muscle belongs to the extensor group. In man and in 

 the dog and many other animals it is an extensor in function. 



