. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 92 COMPARATIVE ANATOMY The columella here also probably arises in connection with the upper end of the hyoid arch (see p. 84), with which it is continuous in Hatteria. The quadrate alone forms as the suspensorium for the lower iaw: it may be articulated witli the skull (Ophidia/ most Lacertilia) or firmly fixed to it (Hatteria, Chelonia, Crocodilia). According to Gaupp, a squamosal is wanting in narrow-mouthed Snakes and Hatteria, and a paraquadrate, comparable to that of the Amphibia (p. 85) is present in almost all L
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 92 COMPARATIVE ANATOMY The columella here also probably arises in connection with the upper end of the hyoid arch (see p. 84), with which it is continuous in Hatteria. The quadrate alone forms as the suspensorium for the lower iaw: it may be articulated witli the skull (Ophidia/ most Lacertilia) or firmly fixed to it (Hatteria, Chelonia, Crocodilia). According to Gaupp, a squamosal is wanting in narrow-mouthed Snakes and Hatteria, and a paraquadrate, comparable to that of the Amphibia (p. 85) is present in almost all Lizards and Chelonians, a quadratojugal being found only in Hatteria. The pterygopalatine arch is well developed in all Keptiles. In Snakes and Lizards it is more or less movable and free from the base of the skull, while in Chelonians and Crocodiles it meets with its fellow to a greater or less extent in the middle line, and shelf-like palatine processes of the maxilla also come into connection with the palatines :—thus a secondary roof is formed to the mouth-cavity distinct from the true (sphenoidal) base of the skull. The cavity thus formed closes in the posterior pro- longation of the nasal chambers, which consequently become sharply differentiated from the mouth. In Chelonians the pterygoid bones do not take part in the formation of this hard folate,, which in Crocodiles is much more markedly developed, and is formed by the premaxillEe, maxillae, palatines, and pterygoids, the posterior nostrils here opening far back into the pharynx (Fig. 75). A number of bones arise in connection with the lower jaw, viz., a dentary, angular, supi-a-angular, splenial, coronoid, and articular. Teeth are well developed in all Reptiles except Chelonians, ^ In Snakes (Figs. 72 and 73) (except Tortrix), the quadrate is only indirectly connected with the skull by means of the squamosal, which extends backwards, and thus throws the articulation of the lower jaw far back, giving rise to a verj'
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