Functional morphology of the hindlimb in some lacertilia.

Based on a global exploration of the hindlimb in some lacertilian species, an equally global functional approach has been undertaken, which led to the concept of the crural mechanism, an integral mechanism comprising the knee joint and the joints between respectively tibia and fibula on the one hand and the astragalocalcaneum on the other. Simple models explain the position of muscles and ligaments in relation to the homonymous rotation of tibia and fibula as well as the relative anterior displacement of fibula in front of the tibia. The linkage of knee and ankle joints appears to be based on those morphological features in both proximal and distal joints, that preclude pure axial rotations of tibia and fibula without deviation of these bones, again in both knee and ankle. The final result appears to be an integral mechanism endowed with one degree of freedom. An attempt has been made to identify the significance of the crural mechanism for function of the hindlimb in sprawling gait.