2. The _middle layer_, _leather-skin_ or _dermis_, is composed of solid, fibrous, and elastic tissues, and contains many blood-vessels, small nerves, sweat-and oil-glands, and hair follicles from which the hair grows. The hair upon the posterior surface of the fetlock-joint is usually long and coarse, forming a tuft known as the “foot-lock,” which encloses a horny spur, called the ergot. Common-bred horses have, as a rule, larger and coarser footlocks than thoroughbreds. The derm or leather-skin, which produces the hair and epiderm, is the thickest and most important layer of the skin. 3. _The inner layer, or subcutaneous tissue_, unites the middle layer with the muscles, tendons, ligaments, bones, or other structures. It is that loose fibrous mesh or net-work through which the butcher cuts in removing the hide from the carcass. [Illustration: FIG. 27. Foot from which the horny capsule or hoof, has been removed by prolonged soaking: _a_, skin; on the left the hair has been rubbed away; _b_, perioplic band; _c_, coronary cushion; _d_, podophyllous tissue (fleshy leaves); at the lower border of the figure can be seen the minute thread-like processes or villi which grow down from the lower end of each fleshy leaf.] (_b_) =The hoof-skin= (Figs. 27 and 28, _b_, _c_, _d_), or pododerm, is completely enclosed by the hoof. Although it is only an extension of the derm or middle layer of the hair-skin, it differs from the latter in structure and relations. [Illustration: FIG. 28. Foot from which the near half of the horny wall and a greater part of the so-called fleshy wall have been removed, in order to show the relation of the lateral cartilage to adjacent structures: _a_, vertical section of the skin prolonged downward through the pododerm (foot-skin) to show clearly that the latter is but a continuation of the former; _a′_, hairless place on the skin; _b_, perioplic band; _b′_, line indicating the upper border of the same; _b″_, surface of section of the periople, or perioplic horn-band; _c_, coronary cushion; _c′_, (left) line which marks the upper border of the coronary cushion; _c″_, section of wall at the toe; _d_, podophyllous tissue (sensitive laminæ); _e_, horny sole; _f_, white line; _g_, horny frog; _h_, fleshy frog; _i_, lateral cartilage.]