The skin is a membrane or external casing of the body. The skin itself consists of two layers covered with hair, fine or coarse, long or short, according to its position or purpose which nature intended it to serve. The outer layer is called the epidermis, the inner the dermis. THE EPIDERMIS.--The epidermis is the outer layer. It is not supplied with nerves and blood vessels, its purpose being to protect the inner layer. This layer undergoes a continual process of being made up and passing away in dandruff. THE DERMIS.--The dermis or true skin lies under the epidermis. It is well supplied with nerves and blood vessels, part of the nerves being the nerves of touch. This fact accounts for its becoming so very sensitive and painful when through injury of any kind the outer layer is scraped off. It is attached to the body by a layer of white tissue known as the areolor tissue, this being that which is cut through when the animal is being skinned. The thickness of the skin varies in different parts of the body, being thinnest in the under parts. The sweat glands are situated in the dermis. THE HAIR. There are three kinds of hair on the horse--the common, the finest of the three, covers most of the body; that of the mane and tail, coarse and long; and that growing on the muzzle or nose and lips, long and usually black, known as tactile or cat hairs. On the inside of the front legs, just above the knee, and on the inside of the hind legs, above the hock, are rough, horny spots. These are called chestnuts. EXPLANATION OF PLATE VII ANATOMY OF THE FOOT.--This illustration represents the foot of a horse sawed from above the fetlock down through the center of the foot. It shows the structure of the foot, the name of each part being given according to number. 1. Lower end of large metacarpal, or cannon bone. 2. Bursa, which secretes the joint oil that lubricates the place where the tendon, or cord, on the front of the leg passes down over the front of the fetlock joint. This is important as it sometimes gets injured and becomes enlarged. It is then called a bursal enlargement, and is of the same nature as a wind gall. 3. Fetlock joint. 4. Os suffraginis, or large pastern bone. 5. Pastern joint. This joint is important; when diseased it is the seat of a high ringbone. 6. Os coronae or small pastern bone. 7. Coffin joint. This joint is important, for when it is diseased it is known as a low ringbone. 8. Wall of the hoof. 9. Os pedis, or coffin bone. 10. Sensitive wall, or quick of the foot. 11. Sensitive sole, or quick of the foot. 12. Frog of the foot, or horney frog. 13. Plantar cushion, or fatty frog. 14. Navicular bone. This is also important, for when diseased it is the seat of navicular, or coffin joint lameness. 15. Back tendons below the fetlock. 16. Sesamoid, or fetlock bones. 17. Skin. 18. Back tendons above the fetlock. [Illustration: PLATE VII. CROSS SECTION OF THE FOOT OF THE HORSE.]