Metatarsal
Long bone of the appendicular skeleton (limb)
Also known as: Hindfoot bone; midfoot bone
Classification
Long bone of the appendicular skeleton (limb)
Dimensions
These are generally elongated bones with a rounded head at one end and a more squared or flared base at the other. In mammals, they are typically longer than the bones of the toes but shorter than the bones of the lower leg.
Key Features
Look for a long, straight shaft with two distinct ends: one end is often rounded like a knuckle to allow for toe movement, while the other end is flatter or more rectangular where it fits against the smaller ankle bones. They are generally more flattened or 'squared off' in cross-section compared to the very round finger bones of the front paw or hand.
Similar Bones
They are easily confused with metacarpals (front foot/hand bones). In many species, hindfoot bones are slightly longer and more slender than their front-foot counterparts. They also resemble phalanges (toe bones), but toe bones are usually much shorter and have more pronounced 'spools' at both ends.
Across Species
The hindfoot bones show incredible variety across the animal kingdom. In humans and bears, these bones rest flat on the ground. In contrast, 'digitigrade' animals like dogs and cats walk on their toes, meaning these bones are held upright and off the ground. In hoofed animals like deer or horses, multiple hindfoot bones have fused into a single, extremely long and strong 'cannon bone' to provide leverage for high-speed running.
Evolutionary History
These structures evolved from the fan-like fin supports of ancient lobe-finned fish. As vertebrates moved onto land, these bones transitioned from paddle elements to structural pillars. Over millions of years, the number of these bones has often reduced in specialized runners; while early land-dwellers had five or more, modern horses have streamlined down to one primary functional bone per leg to reduce weight at the end of the limb.
Photography Tips
To help with identification, place a coin or ruler next to the bone for size reference. Take one photo looking straight down at the flat side, and another from the end to show the shape of the joint surface. Soft, natural light from the side helps highlight the subtle ridges on the shaft.