Calcaneus
Short bone; part of the limb skeleton (appendicular)
Also known as: Heel Bone, hock bone (in quadrupeds)
Classification
Short bone; part of the limb skeleton (appendicular)
Dimensions
Typically chunky and oblong, this bone is often the largest of the ankle group. Its length-to-width ratio varies significantly depending on whether the animal walks on its palms, toes, or hooves.
Key Features
It usually has a blocky, irregular shape with a distinct protruding 'tail' or 'handle' at the back where large tendons attach. One side typically features smooth, scooped-out surfaces where it fits against other ankle bones.
Similar Bones
It is often confused with the Talus (Ankle Bone). However, the Talus is usually smoother and more pulley-shaped, whereas the Calcaneus is more rugged, elongated, and rectangular.
Across Species
In humans and bears, this bone sits flat on the ground to support weight. In contrast, 'digitigrade' animals like dogs and cats have a lengthened heel bone that stays off the ground, acting like a lever for fast running. In hoofed animals like deer or horses, it is very long and forms the prominent 'point' of the back leg, often mistaken for a backwards-facing knee.
Evolutionary History
Originating from early tetrapod ankle structures, the calcaneus evolved into a powerful lever. Over millions of years, as mammals adapted to different environments, this bone specialized—shortening for stability in climbing primates or elongating into a spring-like mechanism for galloping plains-dwellers.
Photography Tips
Place the bone on a neutral background next to a ruler for scale. Capture three views: the top surface showing the smooth joints, a side view to show the handle-like profile, and the back end where tendons would attach.