30 THE ANATOMY OF THE HORSE. 



and flexor tendons. One of them gives off the mitrient artery of the hxrge 

 metacarpal bone. They are of unequal size, the outer being the larger. 



The Digital Veins (Plate 9). These are the satellites of the digital 

 arteries, in front of which they ascend. They drain away the blood 

 from the venous plexuses within the hoof, and, uniting with one 

 another above the fetlock, they foi'm an arch between the deep flexor 

 and the suspensory ligament. From this arch spring the metacarpal veins. 



The Metacarpal Veins are three in number : — 



1. The Internal Metacarpal Vein (Plate 9), which is the largest of 

 the three, ascends in front of the large metacarpal ai'tery, on the inner 

 edge of the flexor tendons. At the inner side of the back of the 

 carpus it is continued as the median vein. 



2. The External Metacarpal Vein is similarly disposed on the outside 

 of the flexor tendons, in company with the external plantar neI•^•e. At 

 the carpus it divides into several anastomosing branches, which are 

 continued as the ulnar and posterior radial veins. 



3. The Interosseotis or Deep Metacarpal Vein is an irregular vessel 

 ascending between the suspensory ligament and the inner splint bone. 

 At the back of the carpus it breaks up into branches that anastomose . 

 with the external and internal metacarpal veins. 



The Plantar Nerves {metacarpal nerves of Percivall). — These are the 

 nerves which confer sensibility on the digit, and which, in their main 

 trunks, or in one of their terminal branches, are cut in the operation of 

 neurotomy. They must therefore be dissected with great care, and the 

 student must make himself thoroughly acquainted with their situation 

 and relations. 



The Internal Plantar Nerve (Plate 7). This is one of the ter- 

 minal branches of the median nerve. Beginning at a variable point 

 above the carpus, it passes within the carpal arch, in close company with 

 the large metacarpal artery, both resting on the side of the deep flexor 

 tendon. Here the nerve crosses beneath the artery, to place itself 

 behind it. Throughout the metacarpal region the same relationship 

 is preserved, the nerve lying immediately behind the artery, in front 

 of which is the internal metacarpal vein. Just above the fetlock the 

 artei'y sinks in somewhat more deeply than the vein and nerve, and 

 thereby allows these to approach each other. In the higher operation 

 of neurotomy the nerve is cut a little way above the fetlock, and before 

 it divides. About the middle of the metacarpus it gives off* a consider- 

 able branch which winds obliquely downwards and outwai'ds behind the 

 flexor tendons, to join the external plantar nerve an inch or more above 

 the button of the splint bone. At the level of the sesamoid bones the 

 tnmk of the nerve divides into thi-ee digital branches, which are 

 distinguished as anterior, middle, and posterior. These are of very 

 unequal size, the posterior being much the largest, and also the most 



