The |radius| is one of the two long bones (the other is the |ulna|) which form the lower arm (forearm). The |radius| articulates at each end with the ends of the |ulna|, with the |humerus| at the elbow, and some of the |carpal bones| at the wrist. When the hand is turned with the palm facing up (called ~supination~), the |radius| is on the lateral (thumb) side of the forearm. When the hand is placed with the palm down (called ~pronation~), the |radius| crosses over the |ulna| in mid-forearm.
