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the horny formation at the ends of the digits of some mammals (chiefly the ungulates), representing a modification of claws. Hoofs consist of walls (corresponding to the nail layer), the soles (or sole layer), and the frogs (the digit cushion), which give way to an L -shaped extended sole. Hoofs developed during adaptation for rapid movement on hard terrain, when the weight was placed on the final joints of the digits. Broad flat hoofs are common to animals that travel primarily on relatively soft terrain (such as northern deer); narrow hoofs that are very hard at the end developed for hard, steep terrain (as in goats). Elephant hoofs have thin walls and cover only the front part of the digit tips.