Bone · Elbow

Radius

Radius

The radius is the thumb-side bone of the forearm, and it is the one that turns. Its disc-shaped head spins in place at the elbow while its lower end swings around the ulna, and that is how the palm rolls from face-up to face-down. Its lower end also forms most of the wrist joint, so the hand effectively hangs off the radius. The biceps inserts on a bump just below the head, which is why bending the elbow and turning the palm upwards are, mechanically, one movement.