THE ANATOMY OF THE HORSE. 



41 



the foot. The inferior border is supported by the wing of the os pedis in 

 front, while posteriorly it blends with the plantar cushion. The anterior 

 border slopes downwards and backw^ards, and is blended with the antero- 

 lateral ligament of the corono-pedal joint. The posterior border is parallel 

 to the anterior, and is covered by the plantar cushion. The four borders 

 meet at four angles, of which the postero-superior one and the one diago- 

 nally opposite are obtuse, while the other two are acute. 



In the disease termed " Side-bones," the lateral cartilages lose their 

 mobility, in consequence of their conversion into bone. 



The Bloodvessels of the Foot (Plate 10, fig. 3). These should be studied 

 in an injected limb from which the hoof has been removed by the method 

 of decomposition described at page 35. The arteries of the foot are 

 derived from the digital artery, which has already been dissected in its 

 descent towards the foot, where, within the wing of the os pedis, it 

 divides into the plantar and preplantar arteries. Some of the collateral 

 branches of the digital artery have already been described at page 29 ; but 

 there remain for examination the artery of the plantar cushion and the 

 coronary circle, as well as the plantar and preplantar terminal branches. 



The Artery of the Plantar Cushion arises from the digital, just as 

 that vessel passes within the upper border of the lateral cartilage, and 

 it passes obliquely downwards and backwards to its destination. Besides 

 supplying the plantar cushion, it gives off a branch which turns forwards 

 to concur in the formation of the circumflex artery of the coronary 

 cushion. 



The Coronary Circle. Where each digital artery lies under cover 

 of the lateral cartilage, it gives off an anterior and a posterior branch 

 which inosculate on the middle line before and behind with the corre- 

 sponding branches of the opposite side, and thus form an arterial circle. 

 This circle closely embraces the os coronse ; and among the largest 

 branches furnished by it, are two which emanate from its anterior half, 

 and descend, one at each border of the extensor tendon, to aid in form- 

 ing the circumflex artery of the coronary cushion. 



The Circumflex Artery of the Coronary Cushion (Chcmveau). This is 

 a slender vascular arch placed immediately above the coronary cushion, to 

 which its branches are distributed. It is fed in front by the two above- 

 mentioned vessels from the coronary circle, and behind, on each side, by 

 the before-mentioned branch from the artery of the plantar cushion. 



The Preplantar Artery is the smaller of the two terminal branches 

 of the digital. It passes forwards through the notch in the wing of the 

 OS pedis, and then along the preplantar groove on the laminal surface of 

 that bone, where its branches are expended in the sensitive laminae. 



The Plantar Artery passes along the plantar groove to enter the 

 foramen of the same name. Within the os pedis it inoscidates with the 

 corresponding vessel of the opposite side, forming the plantar arch, or 



