138 ON THE MORPHOLOGICAL CONSTITUTION OF 



and anchylosed to the lachrymal, sends down a transverse 

 orbito-nasal plate, notched on its inner margin for the olfactory 

 nerve, but separated from its fellow of the opposite side by 

 the pre-sphenoidal processes of attachment of the " palatines." 

 The space roofed over by the nasals and "pre-frontals" is 

 mesially divided above by the contiguous mesial descending 

 laminae of the nasals, and below by the cartilaginous nasal 

 septum. It is floored by the double " vomer," the two halves 

 of which, connected by the lower margin of the cartilaginous 

 septum, extend from the intermaxillaries in front to the cen- 

 trum of the pre-sphenoidal sclerotome behind, being separated 

 from the orbito-nasal processes of the " pre-frontals" by the 

 pre-sphenoidal processes of the " palatines." 



From what has already been stated with reference to the 

 corresponding parts in the bird, the chelonian, and saurian 

 reptile, it will now be seen that I hold the so-called " pre- 

 frontals" of the serpent to be its actual frontals or ethmoido- 

 frontals ; its so-called double " vomer" to consist of the right 

 and left neurapophyses, as the " pre-frontals" are the two halves 

 of the meta-neurapophyses ; and the cartilaginous nasal septum 

 the centrum of its ethmoidal sclerotome. 



The Ethmoidal Neural Arch and Centrum inthe Amphibians. 

 The view which I take of these parts in the Amphibia will 

 at once appear from the foregoing statements, and may be illus- 

 trated by the structure in the frog. As in the bird, the basis 

 of the ethmoidal neural arch and centrum consists of that por- 

 tion of the persistent primordial cranium which is situated 

 behind the intermaxillary region, and immediately in front of 

 the " os a ceinture." The mesial portion of this mass of car- 

 tilage forms the centrum of the sclerotome, as the posterior 

 part of the nasal septum. The posterior portions of the nasal 

 fossae are hollowed out on its sides. Its upper surface is 

 covered by the so-called "pre-frontals," which are, in fact, 

 ethmoidal-frontals, or the two halves of the divided meta- 



