Intermediate Phalanx
This is a Long Bone and is part of the appendicular skeleton (the limbs).
Also known as: Middle toe bone, middle finger bone, or middle pastern bone in ungulates.
Classification
This is a Long Bone and is part of the appendicular skeleton (the limbs).
Dimensions
Typically short and stout, these bones are generally wider than they are long in large mammals, often looking like a small, flared cylinder with a pinched middle.
Key Features
Look for a small, somewhat rectangular bone with a waist-like narrowing in the center. One end usually has a distinct indentation (resembling a shallow saddle) to fit against the bone above it, while the other end is rounded and divided into two soft 'mounds' to connect to the tip of the digit.
Similar Bones
It is easily confused with the first (closest) toe bone, but that bone is typically much longer. It also looks like the very tip toe bone, but the tip bone usually ends in a point or a flat, rough surface for a nail, hoof, or claw rather than a joint.
Across Species
In humans, these are the middle segments of our fingers and toes. In hoofed animals like cows or deer, they are much more robust to support the animal's weight. In horses, this single bone is called the 'short pastern' and is very thick and blocky, while in birds, these bones are elongated and light for grasping or perching.
Evolutionary History
These bones evolved from the simple multi-segmented fin rays of ancient lobe-finned fish. Over millions of years, as animals moved onto land, these segments reduced in number and specialized into the distinct toe and finger structures we see today, adapting for running, climbing, or swimming.
Photography Tips
Place a common object like a coin or a 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.