The tip of a toe of an ungulate mammal, strengthened by a thick horny (keratin) covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole and the edge of the hoof wall. Hooves grow continuously, and are constantly worn down by use. [ https://github.com/obophenotype/uberon/issues/296 http://en.wikipedia.org/wiki/Hoof ]
The hoof is the integument of the foot. Like skin, the integument of the foot has three layers, namely the epidermis, dermis, and SC tissue.