Humerus
Long bone of the appendicular skeleton
Also known as: Upper Arm Bone
Classification
Long bone of the appendicular skeleton
Dimensions
Varies widely by species, featuring a robust central shaft flanked by a rounded ball-shaped joint at one end and a broad, pulley-like articulating surface at the other.
Key Features
Look for a long, sturdy central shaft with one expanded, spongy end that flares out into distinct bumps and ridges. The opposite end typically narrows or shows a rounded contour where it connects to neighboring bones.
Similar Bones
Can be easily confused with the femur (thigh bone) or the tibia (shin bone). The humerus is generally distinguished from the femur by lacking a distinct, sharply angled neck leading directly into a spherical ball joint, and from the tibia by having a more pronounced pulley-like lower end rather than a flat, broad platform.
Across Species
In running mammals like horses and deer, the humerus is relatively short and heavily muscled, tucked close to the chest. In burrowing animals, it becomes exceptionally broad and stout to anchor powerful digging muscles. In marine mammals like whales and dolphins, the humerus is heavily shortened and flattened into a blocky component of the flipper. Birds feature a lightweight, hollow humerus reinforced with internal struts, often containing an air sac connected to the respiratory system.
Evolutionary History
The humerus traces its ancestry back to the paired fins of ancient lobe-finned fish that ventured into shallow waters during the Devonian period. Over hundreds of millions of years, the simple fin rays transformed into a sturdy limb bone capable of supporting body weight on land, eventually diversifying into wings, flippers, and running limbs.
Photography Tips
Place the bone on a neutral, solid-colored background with good side lighting to highlight the texture and contours of the joint ends. Include a common object like a coin or ruler next to the bone to provide a clear sense of scale.