Jaw Muscles of the Crocodiles: Structure, Synonymy, and Some Implications on Homology and Functions

Structure of jaw muscles and their tendons in crocodiles is reviewed. Crocodiles are characterized by following peculiarities of jaw musculature: 1) the jaw adductors consist of the whole muscle mass, and their portions are poorly differentiated; 2) there is large M. pterygoideus anterior ; 3) M. pseudotemporalis is represented by two small bundles of fibers; 4) there is large M. intramandibularis . It is hypothesized, that M. pterygoideus anterior evolved from the main part of the pseudotemporal muscle, by shifting of its site of origin into the orbit. Crocodilian M. intramandibularis may be homologous to the intramandibular belly of the chelonian M. adductor mandibulae internus digastricus . Functions of M. intramandibularis are discussed. Probably, the most important of these is distribution and dissipation of enormous loads applied to lower jaw by the powerful anterio-dorsal jaw adductors.