Radius (bone)

The radius is the bone of the forearm that extends from the outside of the limb to the phlangx (lateral) of the elbow to the thumb side of the wrist. The radius is situated on the lateral side of the ulna, which exceeds it in length and size. It is a long bone, prismatic in form and slightly curved longitudinally. The radius articulates with the capitulum of the humerus.

Sections
Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist-joint.

It has a body and two extremities:


 * Body of radius
 * Upper extremity of radius
 * Lower extremity of radius

Structure
The long narrow medullary cavity is enclosed in a strong wall of compact bone which is thickest along the interosseous border and thinnest at the extremities except over the cup-shaped articular surface (fovea) of the head where it is thickened.

The trabeculae of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli; they are crossed by others parallel to the surface of the fovea.

The arrangement at the lower end is somewhat similar.