Hoof

In Horses, Donkeys and Ruminants, the hoof (Ungula) forms, with the set of organs it contains, the region sometimes imprecisely called 'foot'. It is a corneous box (Capsula ungulae) containing, among other structures, the distal interphalangeal joint (or foot joint) and the distal phalanx (a.k.a. foot bone or coffin bone), as well as shock-absorbing structures.

In Equidae, we recognize three parts to this box: the wall (Paries ungulae), visible externally at all times; the sole (Solea) and the frog (Cuneus ungulae), visible mainly when the hoof is lifted off the ground, the frog being absent in other Ungulates. The proximal part of the wall is covered by a thin, peeling epidermal layer: the periople.