Humerus
Long Bone of the appendicular skeleton
Also known as: Upper Arm Bone
Classification
Long Bone of the appendicular skeleton
Dimensions
Proportions vary widely across species, typically featuring a long central shaft with expanded, bulbous ends designed for muscle attachment and joint articulation.
Key Features
Look for a central cylindrical shaft flaring outward at both ends. One end typically features a smooth, rounded knob for ball-and-socket joint connection, while the opposite end displays a series of ridges and grooves for hinge-like articulation.
Similar Bones
Beginners often confuse long limb bones with each other. The upper arm bone can be distinguished from the thigh bone by its generally smaller size and less massive overall build, and from lower limb bones by having a single dominant shaft rather than being paired alongside a companion bone.
Across Species
In humans, the upper arm bone is built for versatile swinging and tool use. In running mammals like horses, it is tucked closely into the body and built for strength rather than rotation. In swimming marine mammals, it becomes short and stout, helping form a sturdy paddle.
Evolutionary History
The upper arm bone traces its lineage back to the paired fins of ancient lobe-finned fish. Over hundreds of millions of years, as vertebrates transitioned to land, this single foundational skeletal element adapted to support the body weight and facilitate locomotion across terrestrial landscapes.
Photography Tips
Place the bone on a neutral, solid-colored background with good natural side-lighting to cast gentle shadows across its contours. Include a ruler or a familiar household coin next to the specimen for scale, and take shots from both top-down and profile angles to capture the unique shape of the ends.