The trigeminal jaw adductors of primitive snakes and their homologies with the lacertilian jaw adductors

The trigeminal jaw adductor musculature of anilioid snakes is analysed. The group is characterised by primitive characters, viz. the presence of an extensive bodenaponeurosis and of a quadrate aponeurosis. A temporal tendon gives rise to superficial (lb) fibres which are not observed in other snakes: this may be a primitive or a derived feature. Jaw adductor muscles in snakes are usually subdivided following their relative position in an antero–posterior direction. Lacertilian jaw adductors are subdivided in a transverse plane. A detailed comparison of the anilioid and primitive lacertilian jaw adductors establishes correspondences (homologies) of parts in the transverse plane in both groups. These homologies are corroborated by innervational patterns. Platynotan lizards are widely accepted as potential snake ancestors. A comparison of homologue jaw adductors shows different evolutionary trends to characterise platynotan lizards and snakes. Theoretically, these findings do not rule out primitive platynotan lizards as snake ancestors. On the basis of the structure of jaw adductors, snakes are to be derived from a primitive lacertilian pattern, be it platynotan or not.