The calcaneus is the second bone of the first row of the metatarsal bones, situated laterally and plantarly to the talus.
The calcaneus provides the point of the hock with the calcaneal tuberosity that extends proximally from the calcaneus. In ruminants, the calcaneal tuberosity is expanded, roughened and hollowed by a shallow groove. In horses, it is very pronounced and present a mediolateral groove on its proximal surface.
At the dorsal part of the base of the calcaneal tuberosity is a pointed process called the coracoid process.
On the medial side of the base of the calcaneal tuberosity is the sustentaculum tali (talar shelf), a shelf like process that overlaps the plantar aspect of talus and supports the deep digital flexor tendon. On the plantar side of the sustentaculum tali is the groove for tendon of flechissor digitorum lateralis.
The calcaneus present dorsal articular surfaces for the talus, called the talar articular surfaces. In carnivores and horses, these surfaces are separated in two parts by a proximodistal groove called the calcaneal sulcus. The tarsal sinus is the space between the talus and calcaneus, in front of the calcaneal sulcus.
On the distal part of calcaneus is the articular surface for cuboid. On the lateral part is the articular surface for lateral malleolus (malleolar bone in ruminants).