Metacarpal
Long bone, part of the appendicular skeleton
Also known as: Hand bone or foot bone, often referred to as a cannon bone in certain animals
Classification
Long bone, part of the appendicular skeleton
Dimensions
Varies widely from a few inches in small mammals to over a foot in large grazing animals, featuring a sturdy cylindrical shaft with wider, blocky ends.
Key Features
Straight or gently curved solid shaft of dense outer bone material enclosing a central chamber, with squared-off or rounded joint surfaces at both ends.
Similar Bones
Metatarsals from the foot look very similar to metacarpals from the hand. They can also resemble long bone shaft fragments from larger limbs, though the presence of smooth joint surfaces on the ends helps distinguish them.
Across Species
In humans, these form the framework of the palm. In running animals like horses, the middle bone becomes massively enlarged into a single functional unit while the outer ones shrink to tiny splints. In swimming mammals like whales, they lengthen to support broad flippers.
Evolutionary History
Tracing back to early tetrapods, the hand and foot bones evolved from supportive fin rays of ancient lobe-finned fish, gradually adapting from sprawling weight-bearing structures into specialized tools for grasping, running, or swimming.
Photography Tips
Place the bone on a neutral, solid-colored background with natural side-lighting to highlight surface textures. Include a coin or ruler next to the specimen to provide a clear sense of scale.