182 ON THE MORPHOLOGICAL CONSTITUTION OF 



of Professor Owen, are surmounted by the elongated and 

 nearly extruded mastoids ; while the single meta-neurapophy- 

 sis, the undivided " parietal," is so largely developed, that, 

 passing down as in the chelonian to the basis of the cranium, 

 it rests upon the post-sphenoidal centrum over a gi'eat extent 

 in front of its own neurapophyses, so as altogether to 

 obliterate the post-sphenoidal wing. The post-sphenoidal 

 centiTim is there cut off from the post-frontals, which consti- 

 tute the only remaining elements of its neural arch. 



In the lacertians, the occipital centrum, with its pair of 

 neurapophyses and single neurapophysis, is followed by a 

 temporal arch, without a centrum, but with two pairs of neura- 

 pophyses, " petrosals," and mastoids, and an undivided meta- 

 neurapophysis or "parietal," generally single in front, but 

 projecting backwards, with the mastoids on each side behind. 

 The post-sphenoidal centrum is not surmounted by ali-sphe- 

 noids, except the parietal columella represents these elements. 

 The post-frontals again appear ; but without a corresponding 

 me ta-neurapophy sis. 



In the frogs, the occipital centrum and the corresponding 

 meta-neurapophyses have disappeared ; a single pair of neura- 

 pophyses constituting the sole osseous elements of the arch. 

 The temporal centrum appears in the primordial cartilage, 

 which extends across on the upper surface of the posterior 

 part of the much-elongated " basi-sphenoid," and between the 

 cartilaginous auditory capsules. The latter are intimately 

 connected to the inferior temporal neurapophyses, the aH- 

 sphenoids of Professor Owen, wdth which feebly-developed 

 mastoids or superior neurapophyses are conjoined ; the whole 

 being surmounted by the greatly-developed antero-posteriorly 

 elongated so-called " parietals," which dip down slightly at 

 their margins, in front of the temporal region towards the 

 " basi-sphenoid," as in the chelonians and ophidians. The 

 portions of the post-sphenoidal wings and the post-frontals are 



