Radius
Long bone, part of the appendicular skeleton
Also known as: Outer forearm bone
Classification
Long bone, part of the appendicular skeleton
Dimensions
Generally slender and tapers slightly from the lower end up toward the upper end, matching the typical proportions of human forearms.
Key Features
Features a rounded, cup-like shaping at the top end for smooth rotation, and widens significantly at the bottom end where it connects to the wrist area.
Similar Bones
Can be easily confused with the ulna, its parallel partner in the forearm. The radius is generally distinguished by its distinct round head at the top, whereas the ulna typically has a prominent hooked shape.
Across Species
In many mammals, such as cats and dogs, the radius works alongside its companion bone to allow twisting motions of the paw. In animals specialized for running like horses, these bones are fused together to maximize stability during fast movement.
Evolutionary History
Tracing back to early tetrapods stepping onto land, the paired lower-limb bone structure has remained remarkably consistent, adapting over hundreds of millions of years from fins used for navigating shallow waters into weight-bearing and grasping limbs.
Photography Tips
Capture the bone flat against a neutral background from both top-down and profile angles. Ensure bright, even lighting to highlight the curved ends and include a standard ruler for scale.