Let’s start with the forearm, which is the arm between the elbow and the wrist. It supplies the “twisting” of the hand. This rotation around the longitudinal axis of the hand is called the x-axis rotation of the hand. This twisting of the hand is originated in the forearm by the radius rotating around the ulna (Figure 9.1). However, in animation rigs it is often treated as rotation applied directly to the wrist, having nothing to do with the forearm.