DISSECTION OF THE ANTERIOR LIMB. ■ 41 



The Sensitive Sole. The student should next examine that part of 

 the foot which, before separation of the hoof, came into contact with 

 the upper surface of the horny sole, and which for that reason is termed 

 the sensitive sole. It is of a roughly crescentic form, being penetrated 

 by the pyramidal body behind ; and it is co-extensive with the plantar 

 surface of the os pedis. Its connective-tissue basis is firmly adherent to 

 the periosteum of the bone, while its free surface bears long papillae 

 which penetrate the horn tubes of the sole. The horny sole is formed 

 by the agency of the cells which clothe the papillse of the sensitive sole. 



Directions. — On manipulating the bulbs of the plantar cushion, the 

 student will feel the lateral cartilages of the foot ; and one of these is 

 to be exposed and defined by removing one half of the plantar cushion. 



The Lateral Cartilages. These are in the main composed of 

 hyaline cartilage, though, as is common with cartilage in many other 

 regions, it shows a transitional structure at its periphery, where its 

 matrix becomes more or less fibrous. Each plate of cartilage possesses 

 two faces, and four borders separated by four angles. The external fact 

 is convex and covered by a plexus of veins, some of which penetrate 

 the plate and connect the plexus with another lying beneath it. The 

 internal face is concave. Behind it is united to the plantar cushion, 

 while anteriorly it protects the corono-pedal articulation ; and a cul-de- 

 sac of the synovial membrane of the joint lies in direct contact with the 

 cartilage, a fact which it is important to remember in connection with 

 operations for "quittor." The superior border is thin and flexible, and 

 may be felt in the living animal. The digital vessels cross this border 

 in passing into 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 backwards, 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 diagonally opposite are obtuse, A\hile the other 

 two are. acute. 



In the disease termed "Side-bone," the lateral cartilages lo3e 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 36. 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. 



