Phalanx
Long bone, found in the appendicular skeleton as part of the digits
Also known as: Toe bone, Finger bone, or Knuckle bone
Classification
Long bone, found in the appendicular skeleton as part of the digits
Dimensions
These bones are typically much longer than they are wide. In small to medium mammals, they range from the size of a bean to a few inches in length, and they often taper toward one end.
Key Features
Look for a distinct spool-shaped or rounded end that acts like a hinge. The shaft is generally rounded on one side and flatter on the other. One end usually has a shallow depression to receive the rounded end of the next bone in the chain.
Similar Bones
Can be confused with the metatarsals or metacarpals (foot or hand bones). However, those bones are usually much longer and have a more square-shaped base compared to the smaller, more compact toe and finger bones.
Across Species
The variety of these bones across the animal kingdom is a testament to natural selection. In humans and other primates, they remain slender for grasping. In horses, some have evolved into massive, thickened structures that support the animal's entire weight on a single toe, while in bats, they have become incredibly long and thin to stretch out the membranes of the wings.
Evolutionary History
These bones emerged roughly 380 million years ago when fish-like ancestors began transitioning to life on land. Over millions of years, the multi-boned fins of lobe-finned fish rearranged into the standard five-digit limb pattern seen in most land-dwelling vertebrates today.
Photography Tips
Place the bone on a flat, neutral surface next to a coin or a ruler for scale. Take one photo from directly above to show the overall silhouette and another from the end to show the shape of the joint surface.