Form and function in lacertilian knee and mesotarsal joints; a contribution to the analysis of sprawling locomotion

The structure and function of the knee and mesotarsal (ankle) joints in lizards with normally developed limbs is described. It is shown that the knee joint is strictly of the hinge type, but is asymmetrical, resulting in a mesial inflexion of the long axis of the crus relative to that of the femur. The mesotarsal joint is a complex screw joint which permits conjunct rotatory movements of the crus on the pes, as well as flexion-extension. These movements are mediated by interlocking control surfaces on either side of the joint, and are an external expression of the geometry of these surfaces. The morphology of these joints, and the movements they permit are evaluated with reference to the movements of the limb segments during retraction.