The elbow joint connects the bone of the upper arm, the humerus, with the two bones of the lower arm, the radius and the ulna. Within the joint structure are three smaller joints, created by the communication of the three separate bones. The humerus-ulna joint and the humerus-radius joint contribute to the hinge-like motion of the arm. The radius-ulna joint and the humerus-radius joint permit rotation of the forearm and the palm-up, palm-down positioning of the hand.