Humerus
Long bone of the appendicular skeleton
Also known as: Upper Arm Bone, Arm Bone
Classification
Long bone of the appendicular skeleton
Dimensions
Varies widely by species, from a few inches in small mammals to several feet in large quadrupeds, characterized by a distinct rounded top end and a tapering shaft.
Key Features
Look for a smooth, rounded ball-like shape at the top end designed to fit into a socket, a long sturdy shaft, and prominent bumpy ridges along the upper sides where large muscles once attached.
Similar Bones
Can sometimes be confused with the upper leg bone (femur). You can tell them apart because the top of the humerus features a distinctly rounded ball offset by a narrower neck region, whereas upper leg bones generally feature a more sharply angled ball joint setup.
Across Species
In humans and climbing primates, the humerus allows for wide circular arm movements. In running animals like horses and dogs, it is tightly tucked into the shoulder region and built strictly for forward-and-back motion. In whales and dolphins, the humerus has become shortened and stout, hidden inside the flipper alongside other fused arm bones.
Evolutionary History
Tracing back to the earliest land-dwelling four-legged animals, the humerus evolved from the fin bones of ancient lobe-finned fish, adapting over hundreds of millions of years from a paddle-like prop into a versatile lever for walking, running, digging, and flying.
Photography Tips
Place the bone on a solid, neutral-background surface. Take shots of the top end, the full length, and the front and back views under soft, even lighting to highlight surface bumps and textures, including a coin or ruler for size scale.