The forearm consists of two parallel bones, the radius and the ulna. The radius is slightly shorter, running from the thumb side of the wrist to the elbow. The ulna is longer, running from the little finger side of the wrist to the elbow.
The radius and the ulna are connected by the interosseous membrane. Together they are referred to as the radioulnar joint. The radius provides an anchor for the muscles of the upper arm, while the muscles anchored to the ulna provide movement of the arm, hand and wrist. The muscles that attach to both bones are required for everyday activities.