28 THE ANATOMY OP THE HORSE. 



The palmar arterial arches cannot be fully exposed at this stage of the 

 dissection, but it is convenient to describe them here, from their 

 relationship to the vessels of the region. The same applies to the 

 large metacarpal artery and the plantar nerves behind the carpus, 

 all of which can be fully traced in the examination of the carpal sheath 

 (page 34). 



The Large Metacarpal Artery (Plate 9). This is the largest 

 artery in the part of the limb now exposed, and, by means of its ter- 

 minal branches, it is the main vessel of supply to the digit. It has 

 already been seen at its origin, as the larger of the two terminal branches 

 of the posterior radial artery; and, indeed, from its volume and direction, 

 it might be described as the direct continuation of that vessel. From its 

 point of origin at the lower end of the radius, it descends in company 

 with the flexor tendons, by passing behind the carpus and beneath the 

 carpal arch. Emerging from beneath the last-named structure, it con- 

 tinues to descend on the inner side of the flexor tendons until a little 

 above the fetlock, where it sinks slightly inwards to bifurcate into the 

 digital arteries. From the carpus downwards the artery is related to 

 the internal metacarpal vein, which ascends in front of it, and to the 

 internal plantar nerve, which is in contact with it posteriorly. The 

 relative position of the three structures should be carefully noted in 

 reference to the higher operation of neurectomy. Only two of its 

 collateral branches are of suflicient size to merit description, and both 

 are somewhat irregular in their origin. The first of these comes 

 off near the origin of the parent vessel, and may come from the 

 posterior radial itself. It crosses behind the lower extremity of the 

 radius, and anastomoses with the termination of the ulnar artery to 

 form the supracarpal or superficial palmar arch. The second is an 

 un-named vessel which springs from the large metacarpal at or near its 

 point of bifurcation, and divides into branches that ascend to anastomose 

 with the interosseous metacarpal arteries. 



The Supracarpal or Superficial Palmar Arch is formed behind the 

 lower extremity of the radius, by the junction of the above-mentioned 

 branch of the large metacarpal artery with the termination of the ulnar. 

 The convexity of the arch is turned downwards, and from it there arise 

 several branches. The largest and most regular of these descends 

 within the carpal arch, and joins the small metacarpal artery to form 

 the subcarpal or deep palmar arch, which will be dissected at a later 

 stage. 



The Digital Arteries (Plates 9 and 10) are the terminal branches 

 of the large metacarpal artery. They separate at an acute angle, the 

 outer one passing above the fetlock, between the deep flexor and the 

 suspensory ligament. Each passes over the side of the fetlock-joint, and 

 descends at the edge of the flexor tendons as far as the inner face of the 



