Calcaneus
Short Bone, Limb (Appendicular) Skeleton
Also known as: Heel Bone, Hock Bone
Classification
Short Bone, Limb (Appendicular) Skeleton
Dimensions
Generally sturdy and blocky with a long rear-projecting handle. Proportions vary from short and stout in digging animals to long and slender in jumping ones.
Key Features
Look for a rugged, rectangular shape with a long protrusion that resembles a handle or a lever. One end usually has complex, scoop-like surfaces where it fits against the ankle, while the long end provides a rough texture for large tendon attachments.
Similar Bones
It is sometimes confused with the Ulna (the elbow bone) because both have a large 'lever' handle. However, the calcaneus is much blockier and thicker, lacking the long, thin shaft and wrist-joint found on the ulna.
Across Species
In deer and other hooved animals, the calcaneus is much longer than in humans, forming the prominent 'hock' joint visible high up on the back leg. In bears, it is shorter to support a flat-footed walking style. Whales show highly reduced heel bones since they lack hind limbs, while in kangaroos, it is exceptionally long to provide a powerful lever for hopping.
Evolutionary History
This bone emerged as a critical innovation for land-dwelling vertebrates, providing a lever for the muscles that lift the foot. Over millions of years, as mammals specialized for running, this bone elongated to increase mechanical advantage, allowing creatures to spring off their toes more efficiently.
Photography Tips
Place the bone on a plain background next to a coin or ruler for scale. Capture one photo from the side to show the full length of the 'handle' and another looking directly at the articular end where the complex ridges and grooves are visible.