The extent to which the palate is closed in reptiles varies much. In many reptiles, such as the Squamata and Ichthyosauria, the palate is not complete, both palatines and pterygoids being widely separated in the middle line. In others, such as the Crocodilia, Sauropterygia, and Chelonia, there is a more or less complete bony palate. In many Chelonia this is chiefly formed of the vomer, palatines, and pterygoids, the posterior nares being mainly bounded by the palatines. In living Crocodilia, however, outgrowths are formed from the pterygoids and palatines which arch round and meet one another ventrally, forming a secondary palate (fig. 43, A), which completely shuts off the true sphenoidal floor of the skull, and causes the posterior nares which are bounded by the pterygoids to open very far back. Though this feature is common to all postsecondary crocodiles, it is interesting to notice that it is not found in the earlier forms, but that its gradual evolution can be traced. In the Triassic _Belodon_, for instance, the posterior nares open far forwards, and are not surrounded by either the palatines or pterygoids. In the Jurassic crocodile, _Teleosaurus_, the posterior nares lie further back, being surrounded by the palatines, but the pterygoids do not meet them. Finally, in the Tertiary forms the arrangements are as in living crocodiles. A short secondary hard palate is found also in the Theriodontia. The palatines of _Ichthyosaurus_ are noticeable for their transverse position, which recalls that in the Frog. The various =fossae= or =vacuities= in the false roof of the skull are important, and their relations may best be understood by a description of their mode of occurrence in _Sphenodon_, a form in which they are very completely developed. [Illustration FIG. 52. SKULL OF HATTERIA. (_Sphenodon punctatus_). A, lateral; B, dorsal; C, ventral; D, posterior. (After VON ZITTEL.) 1. premaxillae. 2. nasal. 3. prefrontal. 4. frontal. 5. postfrontal. 6. parietal. 7. squamosal. 8. quadratojugal. 9. quadrate. 10. postorbital. 11. jugal. 12. maxillae. 13. vomer. 14. palatine. 15. pterygoid. 16. transpalatine. 17. exoccipital. 18. epipterygoid. 19. basisphenoid. 20. supratemporal fossa. 21. infratemporal or lateral temporal fossa. 22. orbit. 23. post-temporal fossa. 24. foramen magnum. 25. anterior nares. 26. interparietal foramen. 27. dentary. 28. supra-angular. 29. articular.]