Lateral rotation; External rotation

Rotation is a form of movement in which a bone moves around a central axis without undergoing any displacement from this axis; the axis of rotation may lie in a separate bone, as in the case of the pivot formed by the odontoid process of the axis vertebræ around which the atlas turns; or a bone may rotate around its own longitudinal axis, as in the rotation of the humerus at the shoulder-joint; or the axis of rotation may not be quite parallel to the long axis of the bone, as in the movement of the radius on the ulna during pronation and supination of the hand, where it is represented by a line connecting the center of the head of the radius above with the center of the head of the ulna below.