Humerus (Fragment)
Long Bone (Upper Limb)
Also known as: Upper Arm Bone, Wing Bone, Forelimb Bone
Classification
Long Bone (Upper Limb)
Dimensions
In typical medium to large mammals, this bone is thick and robust, usually measuring between 4 to 12 inches long depending on the species, with a notable flared shape at its lower end.
Key Features
This bone is characterized by its cylindrical shaft and distinct rounded 'ball' at the top end. The lower end features a characteristic spool-shaped surface that acts like a hinge. This specific fragment shows the dense outer layer of bone and the sponge-like texture of the inner core.
Similar Bones
It is often confused with the Femur (thigh bone). To tell them apart, look at the top: the femur has a distinct 'neck' before the rounded ball, whereas the upper arm bone's ball sits more directly on the shaft.
Across Species
The upper arm bone is highly adaptable across the animal kingdom. In birds, it is often hollow and light to assist flight; in moles, it is short and incredibly broad for powerful digging; and in humans and primates, it allows for a wide range of circular motion at the shoulder.
Evolutionary History
Tracing back to the first lobe-finned fish that crawled toward land, this bone began as a supportive fin-base element. Over millions of years, it lengthened and strengthened into the primary lever of the forelimb, essential for the transition from swimming to walking on land.
Photography Tips
Lay the bone on a neutral background next to a ruler for scale. Capture one photo looking directly down at the flat side, and another from the end to show the shape of the joint surface.