Metatarsal
Long bone belonging to the limb (appendicular) skeleton
Also known as: Shank bone, Cannon bone (in hooved animals), or Hind-foot bone
Classification
Long bone belonging to the limb (appendicular) skeleton
Dimensions
Typically long and slender compared to its width, with thickened ends for joint connections. In many grazing animals, this bone is significantly elongated to increase stride length.
Key Features
Look for a long, straight shaft with a distinctly shaped lower end that features pully-like grooves (condyles) where it meets the toes. In deer and relatives, a deep vertical groove often runs down the front surface, which is a remnant of where two separate bones fused together during evolutionary history.
Similar Bones
It is easily confused with the metacarpal (front-foot bone). To tell them apart, check the cross-section of the shaft: metatarsals in many herbivores tend to be more square-edged or angular, while metacarpals are often more rounded or D-shaped on one side.
Across Species
In humans, this is one of five small bones in the foot. However, in ungulates like deer, sheep, or cattle, several of these bones have fused into a single, sturdy 'cannon bone.' This adaptation provides a rigid lever for high-speed running. In birds, it fuses with other elements to form the tarsometatarsus, create the long, scaly part of the leg we see above the toes.
Evolutionary History
Over millions of years, the metatarsals of land-dwelling mammals have transitioned from a sprawling, five-toed arrangement used for stability to a more vertical, unified structure used for speed. The fusion of these bones in hooved animals is a classic example of evolutionary streamlining, reducing weight at the end of the limb while increasing structural strength.
Photography Tips
Place the bone on a neutral surface next to a ruler or a common object like a coin for scale. Capture three views: a full-length shot of the front, a side profile, and a close-up of the joint ends (top and bottom) to show the specific shape of the connection surfaces.