172 ON TlIK MORPHOLOGICAL CONSTITUTION OF 



iieurapopliyseal plates (palatal plate of tlie "vomer") wliicli 

 lie soinewliat above the level of the vault of the palate in the 

 tortoises, passing down into, and forming an area of it in the 

 turtles, extending from its posterior margin half-way, or quite 

 up to the intermaxillary palate-plates. In the latter arrange- 

 ment the ethmoidal area is hexagonal, and separates the 

 palatal plates of the maxillaries from one another. In the 

 former it is pentagonal ; and the j)alatal maxillary plates 

 meet in the mesial line in front of it. The palatal plates of 

 the palatines are more or less developed in the turtles ; and 

 many approach one another at the free margin of the vault, 

 but are always separated by the posterior or free margin of 

 the ethmoidal area. 



The arrangement of the vault of the palate in the turtles, 

 and the peculiar chelonian configuration of the pterygoids, 

 lead to the very remarkable combination of ornithic and 

 mammalian structure presented by the nasal fossae and palatal 

 vault of the crocodiles. The mammalian characteristics are 

 the full development of the intermaxillary and nasal bones, 

 with the extensive, although cartilaginous, vomer. The 

 vomerine sclerotome of the crocodile is not closed anteriorly 

 as in all the other lacertians, in the ophidians, amphibians, 

 and birds, but presents a completely perforated catacentric 

 arrangement. This complete form of the vomerine necessitates 

 a rhinal sclerotome, which, accordingly, feebly represented in 

 the crocodiles and alligators, appears to be more fully de- 

 veloped in the gavials. The extensive and complete croco- 

 dilian palatal vault is only apparently mammalian, it is par- 

 tially ornithic or chelonian in its constitution. As in the 

 mammal, the anterior extremity of the vault is formed by the 

 pair of fully formed palatal inter-maxillary plates. Except 

 in the alligators, in which there is a slight intrusion of the 

 ento-pterygoids, the palatal plates of the maxillaries, meeting 

 along the mesial line, form the second and most extensive 



