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.

In Sphenodon, then, on the dorsal surface of the skull, are the large supratemporal fossae (fig. 52, 20). Their inner margins are separated from one another by the parietal walls of the cranium, while externally each is bounded by a bony arch, the supratemporal arcade, formed of the postfrontal, postorbital, and squamosal. Posteriorly the boundary is formed by a post-temporal bar, formed by the parietal and squamosal. Below the supratemporal arcade is another large vacuity, the infratemporal or lateral temporal fossa (fig. 52, 21). This is bounded above by the supratemporal arcade, and is separated from the orbit in front by the postorbital bar, formed by the union of outgrowths from the jugals and postorbitals. Behind it is bounded by a continuation of the post-temporal bar formed of the squamosal and quadratojugal, and below by an infratemporal arcade, which is chiefly composed of the quadratojugal and jugal.

Fig. 52. Skull of Hatteria. (Sphenodon punctatus). A, lateral; B, dorsal; C, ventral; D, posterior. (After von Zittel.)

1. premaxillae.16. transpalatine.
2. nasal.17. exoccipital.
3. prefrontal.18. epipterygoid.
4. frontal.19. basisphenoid.
5. postfrontal.20. supratemporal fossa.
6. parietal.21. infratemporal or lateral temporal
7. squamosal.fossa.
8. quadratojugal.22. orbit.
9. quadrate.23. post-temporal fossa.
10. postorbital.24. foramen magnum.
11. jugal.25. anterior nares.
12. maxillae.26. interparietal foramen.
13. vomer.27. dentary.
14. palatine.28. supra-angular.
15. pterygoid.29. articular.

Below the post-temporal bar is a third vacuity, the post-temporal fossa (fig. 52, D, 23), bounded above by the post-temporal bar and below by the exoccipital and opisthotic.

Sphenodon and the Crocodilia are the only living reptiles with complete supratemporal and infratemporal arcades, but they are both present in the extinct Pterosauria and some Dinosauria.

Supratemporal fossae, bounded below by supratemporal arcades, occur in all reptiles except some Chelonia, the Ophidia, the Geckonidae among Lacertilia, and the Pariasauria and others among Theromorpha; they are specially large in Nothosaurus among the Sauropterygia, Dicynodon among the Theromorpha, and many Crocodilia and Pterosauria. In some Dinosaurs, such as Ceratosaurus, they are very small, while the infratemporal fossae are correspondingly large.

In Elginia[93] (Theromorpha) and some Chelonia, such as Chelone, there are no fossae on the surface of the skull, a complete false roof being developed; in other Chelonia, such as Trionyx, the true cranium is freely visible, the only part of the false roof developed being the infratemporal arcade.