xxi] 



SKULL 



549 



not only in the front part of the cranium but also in the hinder parts 

 of the nasal sac, and is called the sphenethmoid. The parietal 

 is fused with the frontal. 



The suspensorium sends forward a pterygoid process which 

 becomes attached to the skull in the nasal region. Underneath the 

 posterior part of the pterygoid process there is a pterygoid bone 

 which surrounds it and partly replaces it. The pterygoid sends out 

 a fork which underlies that part of the suspensorium which forms 

 an articulation for the lower jaw. The front part of the pterygoid 

 process where it bends in to rejoin the skull is ossified by the 

 palatine, which like the pterygoid has become a cartilage bone. 

 The palatine is transverse to the axis of the skull, as in Ambly- 

 stoma. Neither palatine nor pterygoid bears teeth, but the vomers 

 bear a little group of teeth towards their hinder edge. These 

 vomerine teeth are used for crushing the food, and are present in 

 species like the Toad where the teeth borne by premaxillae and 

 maxillae have been lost. 



The upper lip has a series of 

 three bones on each side, reach- 

 ing completely to the suspen- 

 sorium, an additional quadra- 

 tojugal being added to the 

 two present in the Newt. The 

 presence of this bone suggests 

 that the ancestors of the Anura 

 are to be sought amongst that 

 highly modified group of the 

 Stegocephala termed the Laby- 

 rinthodonta. In them as in the 

 Anura the ventral inter-calary 

 element was absent but at any 

 rate in the earlier forms the 

 basidorsals, the basiventrals and 

 the interdorsals were distinct 

 pieces. In all Anura there is a 

 large m embrane bone of a charac- 

 teristic T-shape, known as the 

 squamosal, lying outside the 

 suspensorium. In the lower lip 

 there is a splenial and a dentary, 

 whilst in front the cartilaginous 

 lower jaw is replaced by a pre- 



FIG. 270. A. Lateral view of the skull 

 of a Common Frog, Rana temporaria 

 x 2. B. Posterior view of the skull of 

 the same. Both figures after Parker. 



1. Sphenethmoid. 2. Frontoparietal. 

 3. Pterygoid. 4. Squamosal. 5. Tym- 

 panic membrane. 6. Exoccipital. 

 7. Parasphenoid. 8. Pro-otic. 



9. Quadratojugal. 10. Maxilla. 



11. Nasal. 12. Premaxilla. 13. An- 

 terior nares. 14. Predentary. 



15. Dentary. 16. Splenial. 17. Basi- 

 lingual plate. 19. Quadrate. 



20. Columella. 21. Occipital condyle. 

 22. Anterior cornu of the hyoid (cerato- 

 hyal). 23. Foramen magnum. ir, 

 ix, x. Foramina for the exit of cranial 

 neives. 



