Fig. 27. Dorsal view of the skull of a Labyrinthodont (Capitosaurus nasutus) × 1/9 (from von Zittel).

1. premaxillae.12. postorbital.
2. nasal.13. interparietal foramen.
3. maxillae.14. squamosal.
4. anterior nares.15. supratemporal.
5. frontal.16. quadratojugal.
6. prefrontal.17. quadrate.
7. lachrymal.18. epi-otic.
8. jugal.19. dermo-supra-occipital.
9. orbit.20. exoccipital.
10. parietal.21. foramen magnum.
11. postfrontal.

Labyrinthodontia. The skull in Labyrinthodontia is remarkable for its extreme solidity, the large number of bones which are present, and the extent to which the roofing over of the temporal and other fossae has taken place. In many forms the surface of the bones is as in Crocodiles, strongly sculptured (fig. 27, right half) with ridges and grooves which probably lodged sensory organs. The bones forming the roof of the skull are generally very uniform in size, perhaps the most noticeable of them being the paired dermo-supra-occipitals (fig. 27, 19). Paired dermo-supra-occipitals occur also in certain Ganoids. The Labyrinthodont skull also bears resemblance to that of many fish in the development of a pair of long pointed epi-otics (fig. 27, 18), which remain permanently distinct from the surrounding bones. The parietals are small and enclose between them the interparietal foramen (fig. 27, 13). In some forms in which the head is protected with an armour of scutes, these do not roof over the interparietal foramen, and from this fact it has been inferred that the Labyrinthodonts had a functional pineal eye. Both supra- and infra-temporal fossae are partially or completely roofed over by the postorbitals and large supra-temporals (fig. 27, 15).

There is generally a ring of bones in the sclerotic coat of the eye. The pterygoids do not meet in the middle line, being separated by the parasphenoid. The palatines bear teeth, and in some genera (Archegosaurus) form long splints lying along the inner side of the maxillae and more or less surrounding the posterior nares. In others (Nyrania) they lie in the normal position near the middle line, one on each side of the parasphenoid. The vomers bear teeth and sometimes meet in the middle line; they are sometimes confluent with the parasphenoid. On the ventral surface of the cranium there are generally large palatal vacuities.

In the mandible there is often a well-marked postglenoid process, and the articular is generally completely ossified.

Fig. 28. A, ventral view of the cranium; B, lateral view of the cranium and mandible of Siphonops annulatus (after Wiedersheim).

1. anterior nares.9. squamosal.
2. naso-premaxillae.10. exoccipital.
3. frontal.11. dentary.
4. parietal.12. angular.
5. maxillae.13. basi-occipital and
6. vomer.basisphenoid fused.
7. orbit.14. posterior narial opening
8. quadrate united with thesurrounded by the palatine.
pterygoid in front.X. pneumogastric foramen.

Gymnophiona. The skull bears a considerable resemblance to that of Labyrinthodonts, especially in the arrangement of the bones which bound the mouth cavity. The cranium is very hard, and is covered by a complete bony roof formed mainly of the exoccipitals, parietals, frontals, prefrontals, nasals and premaxillae. The nasals and premaxillae are sometimes ossified continuously. There is a median unpaired ethmoid whose dorsal end appears at the surface wedged in between the frontals and parietals. The bone generally regarded as the squamosal[63] is very large, and it and the maxillae generally together surround the orbit, which, in Epicrium, has in it a ring of bones. The palatines form long tooth-bearing bones fused with the inner sides of the maxillae; they nearly surround the posterior nares.