Answer: lateral
The radius is a long bone in the forearm. In anatomic position, it lies lateral to the ulna, which is smaller than the radius. Both radius and ulna connect to the humerus bone of the upper arm at the elbow joint. The radius pivots around the ulna to create movement at the proximal and distal radio-ulnar joints. Moreover, radius articulates in elbow joint, proximal radioulnar joint, wrist joint and distal radioulnar joint.