wear naturally from sufficient movement on abrasive terrain, then it will protrude from the solar surface. It then becomes prone to breakage, and the healthy hoof will self-trim by breaking or chipping off. When a horseshoe is applied, it is fixed to the wall. Nails are driven in, oblique to the walls. They enter the wall at the outside edge of the white line and they emerge at the wall's surface, about 15 to 20 mm from the base of the wall. The wall is anatomically analogous to the human fingernail or toenail. The frog The frog is a V-shaped structure that extends forward across about two-thirds of the sole. Its thickness grows from the front to the back and, at the back, it merges with the heel periople. In its midline, it has a central groove (sulcus) that extends up between the bulbs. It is dark gray-blackish in color and of a rubbery consistency, suggesting its role as a shock absorber and grip tool on hard, smooth ground. The frog also acts like a pump to move the blood back to the heart, a great distance from the relatively thin leg to the main organ of the circulatory system. In the stabled horse, the frog does not wear but degrades, due to bacterial and fungal activity, to an irregular, soft, slashed surface. In the free-roaming horse, it hardens into a callous consistency with a near-smooth surface. For good health, the horse requires dry areas to stand. If exposed to constant wet or damp environments, the frog will develop a bacterial infection called thrush. The frog is anatomically analogous to the human fingertip. The sole The sole has a whitish-yellowish, sometimes grayish color. It covers the whole space from the perimeter of the wall to the bars and the frog, on the underside of the hoof. Its deep layer has a compact, waxy character and it is called 'live sole'. Its surface is variable in character as a result of ground contact. If there is no contact, as in shod hooves or when the walls are too long or the movement poor, the lower surface of the sole has a crumbly consistency, and it is easily abraded by scratching it with a hoofpick. Conversely, it has a very hard consistency, with a smooth, bright surface, when there is a consistent, active contact with the ground. The front portion beneath the