DEVELOPMENT OF THE SKULL OF EMYS 751 



The antero-ventral margin of the parietale Hes parallel to the 

 free margin of the planum supraseptale at a short distance dor- 

 sal and lateral to it, while its anterior angle comes to he medial 

 to the posterior end of the frontale. The posterior margin of 

 the parietale rests with its projecting processus occipitahs against 

 the anterior cupola of the otic capsule. 



The frontale is a narrow, curved plate that continues the con- 

 tour of the parietale forward. Its ventral margin, like that of 

 the parietale, lies parallel to the free margin of the planum 

 supraseptale and completes the orbit dorsaUy. Its posterior end 

 overlaps laterally the anterior end of the parietale and its 

 extreme anterior end is embraced by the dorsal extremity of 

 the praefrontale. 



In contrast to the condition in Lacerta the frontale in Emys 

 extends less far posteriorly so that it fails to be overlapped by 

 the anterior extremity of the postfrontale. The frontale at this 

 stage of development is relatively small, its place being taken to 

 a certain extent by the extremely large praefrontale in front and 

 the unusually large parietale behind. 



The praefrontale (p/.) or lacrimale is very large, completing 

 the orbit anteriorly and embracing the greater part of the olfac- 

 tory capsule. In form it exhibits a vertical plate which extends 

 beyond and lateral to the antero-ventral end of the frontale, 

 and a larger obhque portion lateral to the olfactory capsule and 

 lying dorsal to the anterior portion (processus praefrontahs) of 

 the maxillare. The anterior margin of the vertical limb of the 

 praefrontale becomes very thick, so that there is a distinct ante- 

 rior, as well as a lateral and a medial face. It may be that 

 this thickening of the dorsal portion of the praefrontale stands 

 in connection with the fact that a nasale is lacking. 



The pterygoideum {pt.) is strongly developed in the stage of 

 Emys modelled, and exhibits clearly many of the characteristics 

 of the adult form. It is a long, slender bone with ventral face 

 extending horizontally and a longitudinal crest, the crista ptery- 

 goidea {c.pt., fig. 20), extending dorsally, which diminishes in 

 height from posterior to anterior and separates the fossa supra- 

 pterygoidea, lying lateral to it, from the sulcus cavernosus on 



