. . "Base member 5150 is preferably formed of a mechanically suitable, biologically compatible plastic or metal such as polyurethane or titanium and preferably configured to correspond to the machined vertebrae end plate configuration illustrated, for example, in FIGS. 69C and 70E wherein a semicircularly-shaped surface portion 5192 thereof corresponds to recess 2672 and a generally cylindrical extensi" . . .