Calcaneus
Short Bone, Appendicular Skeleton
Also known as: Heel Bone, Hock Bone
Classification
Short Bone, Appendicular Skeleton
Dimensions
Typically longer and more robust than other ankle bones, it often features a prominent, rectangular extension at the back that serves as a lever.
Key Features
It is easily recognized by its distinctive boot-like or hammer shape. Look for a large, rough block at one end that tapers into a narrower neck, and a grooved surface on the front where it connects to other ankle bones.
Similar Bones
It can be confused with the Astragalus (Talus), which is another large ankle bone. However, the Calcaneus is generally longer with a clear projecting 'handle' or heel, whereas the Astragalus is more rounded or pulley-shaped.
Across Species
In mammals, the size and length of this bone vary based on movement style. In high-speed runners like deer or horses, it is long and thin, creating a powerful lever for rapid springing. In plant-eating mammals that stand flat-footed like bears or humans, it is sturdier and broader to support the weight of the entire body.
Evolutionary History
This bone evolved from a series of small, pebble-like bones in the ankles of early land-dwelling tetrapods. Over millions of years, it enlarged and fused to provide a dedicated attachment point for large leg muscles, allowing vertebrates to push off the ground with greater force during walking and running.
Photography Tips
Place the bone on a plain surface and photograph it from the side to show its full length and 'hammer' profile. Use a coin or ruler next to it for scale, and try to capture the texture of the blocky end where muscles once attached.