Humerus
Long Bone, part of the limb (appendicular) skeleton
Also known as: Upper Arm Bone
Classification
Long Bone, part of the limb (appendicular) skeleton
Dimensions
Varies widely by species, ranging from a few inches in small mammals to over two feet in large ungulates. It typically features a sturdy central shaft flanked by broader, flared ends designed for joint connections.
Key Features
Characterized by a long central shaft with wide, flared ends. One end usually features a smooth, rounded knob or pulley-like shape for articulating with neighboring bones, while the interior reveals a honeycomb-like network of spongy bone exposed where the outer shell is open.
Similar Bones
Can be easily confused with the thigh bone (femur) or the lower leg bones (tibia). The upper arm bone is generally distinguished by the specific rounded shape of its upper joint end and the twist or curve of its central shaft.
Across Species
In humans and climbing primates, the upper arm bone allows for a wide range of shoulder movement. In running mammals like horses and dogs, it is tucked tightly against the body and built for forward-and-back stride efficiency. In whales and dolphins, the bone has been shortened and flattened to function as a rigid paddle inside the flipper.
Evolutionary History
The upper arm bone traces its lineage back to the paired fins of ancient lobe-finned fish, possessing the classic one-bone structural blueprint that made the transition to land possible hundreds of millions of years ago.
Photography Tips
Place the bone on a neutral, solid-colored background with a coin or ruler next to it for scale. Take one straight-down photo showing the entire length, and a second close-up photo focusing on the textured inner spongy structure and the wide ends.