154 ON THE MORPHOLOGICAL CONSTITUTION OF 



of birds ; and I find in the Asiatic Cassowary, the stage imme- 

 diately preceding the completion of the process in Apteryx. 

 In this bird, the pair of deep fossaj in the interior of the skull, 

 which lodge the olfactory lobes, are separated from one an- 

 other by the posterior margin of the pre-sphenoidal centrum, 

 which here represents the crista galli. The plate of bone which 

 forms the floor of each fossa, instead of being cribriform, as in 

 Apteryx, is perforated by a single star-like foramen, a form due 

 to the partial shooting across of bony processes from its margin. 



In the Ghelonian. — The neural arch and centrum of the 

 chelonian are represented in the dry skull by the pair of 

 bones usually considered as the " proper frontals," but which 

 I regard as sphenoido-frontals. In the recent condition the 

 centrum appears in the form of a compressed cartilaginous 

 bar, continuous posteriorly with the compressed anterior part 

 of the post-sphenoidal centrum, resting below on the conjoined 

 pterygoids and ento-pterygoids, continuous in front with the 

 cartilaginous ethmoidal septum or centrum, and thus pre- 

 senting all the relations of the pre-sphenoidal centrum of the 

 bird. It is continued upwards, and represents the orbito- 

 sphenoids, or neurapophyses, in the form of a double fibro- 

 cartilaginous membrane, the two laminae of which separate to 

 unite with the posterior margins of the orbito-nasal processes of 

 the ethmoido-frontals, with the two parallel descending ridges 

 of the sphenoido-frontals, and with the anterior margins of the 

 peculiar descending processes of the so-called " parietals." The 

 olfactory nerves pass forwards between these neurapophyseal 

 laminse above ; and the optic, with the other orbital nerves, 

 perforates them. 



In the Crocodilian. — In the crocodiles, the sphenoido- 

 frontals have coalesced ; but the cartilaginous centrum and 

 neurapophyseal interorbital lamime present exactly the same 

 relations as in the chelonian ; the only difference being the 

 result of the union of the orbito-nasal processes of the 



