What is the ulnar surface that articulates with the radial head?

The ulnar surface that articulates with the radial head is known as the ulnar notch of the radius. This is a concave area located on the distal end of the radius, where it meets the head of the ulna at the wrist. The articulation between the radial head and the ulnar notch allows for the rotational movement of the forearm, including pronation and supination. This joint is crucial for the overall function and stability of the forearm and wrist.