THE SKELETON UF THE VKI;TEI:1:ATE HEAD. 171 



The external nostrils of the lacertian, ophidian, and ani- 

 phihian, are situated, as in the bird, between the vomerine 

 and ethmoidal sclerotomes ; the intennaxillaries being closed 

 in front and below. The so-called nasal fossie in these verte- 

 brate forms are also, as in the bird, merely olfactory chambers, 

 occupyijig the neural space of the ethmoidal sclerotome. Tlie 

 posterior narcs, too, open as in the bird, between the eth- 

 moidal and pre-spheuoidal sclerotomes, but -with the follow- 

 ing subordinate diifereuces : — In the li/ard they are separated 

 by the anterior extremities of the ento-pterygoids, and arc 

 bounded behind by the maxillary processes of these bones, 

 and externally by the maxilhiries themselves. In the ophidian 

 they are separated by the free margin of the ethmoidal cata- 

 ceutric plates ; anteriorly by the posterior margins of the eth- 

 moidal neurapophyses, externally by the anterior j»rojecting 

 portions of the ento-pterygoids, and beliind by the pre- 

 sphenoidal attachments of the latter. In the frog they open 

 between the ethmoidal neurapophyses (" vomer"), the ento- 

 pteiygoids (" palatals "), and the maxillaries. 



"We again approach the mammalian type of nasal fossa?, 

 through the tortoises, turtles, and crocodiles. 



It has been already stated that the anterior nostrils of the 

 Chelonian appear to possess more of the ornithic than mam- 

 malian confoi-mation. The primordial cartOaginous lining of 

 the olfactory fossas projects in some turtles through the an- 

 terior nasal opening of the cranium in the form of a double 

 proboscis. The posterior nares in the tortoises are separated 

 by the combined ento-pteiygoids (upper and back part of the 

 " vomer"), and are bounded by the maxillaries and the pala- 

 tines, the latter remaining open or ununited across tlie vault 

 of the palate. In the tui-tles, the vault of the palate and the 

 posterior nares present more of the mammalian aspect, 

 althouiih stdl formed esscntiallv on the tvi>e of the conv- 

 Spending parts in the bird. Tiiis is ellecteil by the ethmoidal 



