THE SKELETON OF THE VERTEBRATE HEAD. 137 



bones, which form the floor of the nostrils, separated from, 

 but at the same time connected to, one another by the lower 

 margin of the cartilaginous nasal septum, abutting against the 

 intermaxillaries in front, and the so-called "palatines" or 

 ento-pterygoids behind, and leaving a space on each side, 

 wider behind than before, between their outer margins and 

 the maxillaries, for the posterior nares. In some lizards the 

 posterior extremities of the two halves of the " vomer" are 

 separated from the transverse descending plates of the " pre- 

 frontals" by the interposition of the anterior extremities of 

 the ento-pterygoids, but in others they articulate with the 

 pre-fronto-lachryrnal. Anatomists appear to have been in- 

 duced to look upon these two bones in the lizard as the two 

 halves of the vomer, by the same circumstance which has 

 induced them to consider the ento-pterygoids of the bird as its 

 vomer viz. their position between the posterior nares. But 

 the general relations of the so-called double "vomer" of the 

 lizard indicate that its two halves are homologous with the 

 ethmoidal palate-plates of the chelonian, with the so-called 

 "palatines" or ethmoidal neurapophyses of the crocodilian, 

 with the corresponding cartilaginous or osseous pieces in the 

 bird, and with the lateral masses of the ethmoid in the mam- 

 mal. It appears to me that the ethmoidal neural arch and 

 centrum form a catacentric arrangement, the two compart- 

 ments of which constitute the greater part of the nasal fossae, the 

 olfactory nerves entering through the mesially divided space 

 between the descending or orbito-nasal processes of the meta- 

 neurapophyses ; and the posterior nares passing off on the outer 

 sides, and between the neurapophyses and the maxillaries. 



The Ethmoidal Neural Arch and Centrum in Ophidians. 

 The maxillaries of the serpent are articulated or connected to 

 the " pre-frontals." The latter are separated from one another 

 mesially by the elongation of the nasals back to the " principal 

 frontals." Each of the "pre-frontals," comparatively large 



