Types and Market Classes of Live Stock 



409 



fibro-fatty tissue filling all the space between the lateral cartilages, 

 forming the fleshy heels, and serving as a buffer to disperse shocks. 

 It extends forward underneath the navicular bone and flexor tendon, 

 and protects these structures from injurious pressure from below. 



The pododerm or hoof-producing membrane is merely a continua- 

 tion of the derm, or true skin. It covers the foot inside the hoof, just 

 as a sock covers the human foot inside the shoe. It differs from the 

 ordinary external or "hair" skin in having no sweat or oil glands, but, 

 like it, is richly supplied with blood vessels and sensitive nerves. The 

 functions of the pododerm are to produce the hoof and unite it firmly 

 to the foot. 



The hoof and how it grows. — The horny shell, called the hoof, 

 which covers and protects the foot, is made up of three parts, (1) the 

 wall and bars, (2) the sole, and (3) the frog. Each part of the hoof 



Fig. 153. — Diagram showing structure of foot. 1, Coffin bone; 2, small pas- 

 tern bone; 3, large pastern bone; 4, navicular bone; 5, lateral cartilage; 6, extensor 

 tendon; 7, flexor tendon of foot; 8, flexor tendon of pastern; 9, branches of suspensory 

 ligament; 10, wall; 11, sole; 12, frog; 13, indicates location of plantar cushion between 

 the lateral cartilages; 14, perioplic ring; 15, coronary cushion. 



is grown by some particular part or parts of the pododerm. In general 

 it may be said that the horn of the hoof is made up of tubules or shafts 

 of horn which grow from papillae the same as does hair. These 

 tubules are cemented together by non-tubular matter corresponding 

 to dandruff exfoliated by the skin. In fact, so pronounced is the 

 similarity in growth of horn and hair that coarse hair, especially on 

 the legs and coronet, is associated with horn of coarse texture. There- 

 fore the more coarse and brittle the hair about the coronet, the more 

 porous, brittle, and weak will be the formation of the horny hoof. ^ 



The wall horn consists of three layers known as (1) the outer or 

 perioplic layer, (2) the middle or coronary layer, and (3) the inner or 



ij. H. S. Johnstone: The Horse Book, p. 24. 



