The ontogenetic development of the jaw adductor musculature in Natrix natrix (L.) is described in detail and related to patterns of ossification in the skull. A comparison with the development of the jaw adductors in the lizard Podarcis sicula reveals some interesting differences of dynamics in the developing head. The problem of the establishment of topological relations of similarity (homology) in developing systems is discussed.
The homologies of the external jaw adductor compartments in lizards and snakes are revised. Early ontogenetic divergence explains the reversal of fibre direction in the anterior portion of the external adductor of snakes, and renders the homologization of that fibre bundle with part of the external adductor in lizards impossible.