Fig. 3

The process of the generation of the instantaneous rotation axis. Three dots which were located in the highest depression were registered and the plane which went through three dots was brought out (Fig. 3A). A curve went through the ulna surface and fitted the polyline which was the intersection of the plane and the surface of the ulna (Fig. 3B). The instantaneous rotation axis was generated by connecting the center of 11 curves (Fig. 3C)