The skulls of _Megalobatrachus_, _Cryptobranchus_ and _Siredon_ resemble those of the highest Urodeles the Salamanders in their wide form, in having the pro-otics distinct from the exoccipitals which are ossified continuously with the epi-otics and opisthotics, and in having no palatines, but differ in having the two premaxillae separate, and in the arrangement of the vomerine teeth which in _Megalobatrachus_ and _Cryptobranchus_ are placed along the anterior boundaries of the bones, these meeting in the middle line. In _Siredon_ the vomers are separated by the very large parasphenoid. The suspensorium in _Megalobatrachus_ and _Cryptobranchus_ projects at right angles to the cranium; in _Siredon_ it projects somewhat downwards and forwards as in the Salamandrina. Modifications of the vomers, pterygoids and palatines accompany the changes of the larval ichthyoid _Siredon_ into the adult salamandroid _Amblystoma_, the vomers especially come to resemble to a much greater extent those of the Salamandrina. The ossification of the skull in the Salamandrina is carried further than in the Ichthyoidea, though the supra-occipital and basi-occipital are not ossified. The skull differs from that in the Ichthyoidea in the size of the part of the vomero-palatines which lies in front of the teeth, in the frequent union of the two premaxillae and in the ossification of all the periotic bones continuously with the exoccipital. The skull differs from that of Anura in the following respects:-- (1) the bones of the upper jaw do not form a complete arch standing away from the cranium, and the maxillae are not united to the quadrates by quadratojugals, (2) the long axis of the suspensorium passes obliquely downwards and forwards instead of downwards and backwards, (3) there is no sphenethmoid encircling the anterior end of the brain, its place being partly taken by a pair of orbitosphenoids, (4) there is no definite tympanic cavity. [Illustration FIG. 27. DORSAL VIEW OF THE SKULL OF A LABYRINTHODONT (_Capitosaurus nasutus_) × 1/9 (from VON ZITTEL). 1. premaxillae. 2. nasal. 3. maxillae. 4. anterior nares. 5. frontal. 6. prefrontal. 7. lachrymal. 8. jugal. 9. orbit. 10. parietal. 11. postfrontal. 12. postorbital. 13. interparietal foramen. 14. squamosal. 15. supratemporal. 16. quadratojugal. 17. quadrate. 18. epi-otic. 19. dermo-supra-occipital. 20. exoccipital. 21. foramen magnum.]