Metatarsal
Long bone; part of the limb (appendicular) skeleton
Also known as: Lower hind-limb bone, Cannon bone (in ungulates), Hind foot bone
Classification
Long bone; part of the limb (appendicular) skeleton
Dimensions
In large mammals like deer or cattle, these are long, sturdy tubes. They are typically narrow compared to their length, with thickened, flared ends where they meet other joints.
Key Features
Look for a long, straight shaft with a distinctly squared or flattened cross-section in some species. The bottom end usually features two rounded, pulley-like knobs separated by a central ridge, which allows the toes to hinge smoothly. The top end is typically flatter with small facets where it tucked against the ankle bones.
Similar Bones
This can be confused with a Metacarpal (front foot bone). Generally, the Metatarsal has a more squared or rectangular cross-section in the shaft, whereas the Metacarpal of the front limb tends to be more D-shaped or rounded toward the front surface.
Across Species
The shape of this bone tells a story of how an animal moves. In humans, we have five separate metatarsals forming the arch of the foot. In contrast, grazing animals like horses or deer have fused these into a single, powerful 'cannon bone' to provide a lightweight but strong lever for high-speed running. Birds have a similar adaptation where this bone is fused with ankle bones into a 'tarsometatarsus,' which is the long part of the leg above the toes.
Evolutionary History
Metatarsals began as small, separate bones in the feet of early land-dwelling vertebrates. Over millions of years, as different lineages specialized for speed, climbing, or swimming, these bones shifted. In many running mammals, the outer toes were lost and the remaining central foot bones elongated and strengthened to allow the animal to walk on its tip-toes, effectively lengthening the leg for a more efficient stride.
Photography Tips
Lay the bone on a flat surface and take a photo from directly above to show the overall length. Be sure to include a clear close-up of the joint surfaces at both the top and bottom ends. Placing a common object like a coin or a ruler next to the bone helps viewers understand its true scale.