40 DISSECTION OP THE ANTERIOR LIMB. 



surface, and it is moulded on the upper face of the horny frog, to which 

 it has a close resemblance in form. The central portion of the cushion 

 is therefore sometimes termed the sensitive frog, and it is also known as 

 the pyramidal body. It shows in front a single ridge, which posteriorly 

 becomes divided into two by a deep median cleft for the reception of 

 the frog-stay. This surface has a villous aspect, the papillae being 

 imbedded in the foramina seen on the upper surface of the horny frog. 

 The horny frog is formed by the agency of the cells covering these 

 papillae. The u^pper face looks forwards as well as upwards, and is 

 applied to the reinforcing sheath of the deep flexor tendon. The 

 borders, which are right and left, bring the plantar cushion into relation 

 with the inner surface of the lateral cartilages. The ape.K lies in front 

 of the semilunar crest of the os pedis, with whose periosteum the tissue 

 of the cushion is intimately blended. The base of the cushion consists 

 of two thick rounded masses termed the hulbs of the plant9,r cushion. 

 These are continuous in front with the ridges of the pyramidal body, 

 and they present the same velvety aspect ; while, on each side, the . 

 villous tissue joins the extremities of the coronary cushion. 



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 crescentio 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 papillse 

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

 by the agency of the cells which clothe the papillte 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 often erroneously termed the fibro-cartilages of 

 the foot. As is common with fibro-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 face is convex and 

 covered by a plexus of veins, some of which penetrate the plate and 

 contiect 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 fot 

 "quitter." The superior border is thin and flexible, and may be felt in 

 the living animal. The digital vpmoIs cross this border in passing into 



