624 JOHN D. KERNAN, JR. 



cranial pole of the cochlea, which he called the supra-cochlear 

 cartilage. DeBurlet, in his examination of the primordial 

 cranium of the whale, demonstrated that the commissura ali- 

 cochlearis, to which that nodule probably belonged, was outside 

 the primitive skull. Examination of the sections show the 

 beginning of the formation of the side wall lateral to the Gas- 

 serian ganglion in the form of a dense blastema which passes from 

 the outer side of the pars canalicularis craniad a variable dis- 

 tance to the outer side of the skull vault. In such of the lower 

 mammals as I have examined (cat, opossum, Tupaia) this pro- 

 cess is cartilage, and in them forms the parietal plate dorsally 

 and the commissura orbito-temporalis ventrally, which is homol- 

 ogous to the taenia marginata of reptiles (figs. 5 and 7). 



As concerns its cartilage, the ethmoid region is very rudimen- 

 tar5^ The mesethmoid consists of a mesially placed plate of 

 cartilage which begins dorsally as a triangular bar with its base 

 against the cranial surface of the sphenoid body, and its apex 

 projecting upward in front of the lamina hypochiasmatica (figs. 

 1, 2 and 7). In this region, as Macklin points out, it forms the 

 inter-orbital septum, homologous to the inter-orbital septum of 

 reptiles. As it extends forward, the base of the triangle narrows, 

 and distally it forms a flat nasal septum. This gradual flat- 

 tening can be followed in the sections. At the cranial extremity, 

 the dorsal edge protrudes upward to form the anlage of the crista 

 galli (fig. 2). From the ventral edge of the septum project two 

 slender ridges of pre-cartilaginous tissue which are the anlages 

 of Jacobson's cartilages (fig. 9, A). They are not connected with 

 the cartilage of the septum, but appear to be in a sheet of dense 

 blastema which extends dorsally on each side of the septum 

 (fig. 3). 



The ethmoid region presents laterally two small flat plates of 

 cartilage with their dorsal edges inclining toward the septum 

 (fig. 9, A). There is only slight indication as yet of cartilaginous 

 turbinates. 



Rudimentary as is the cartilage, the nasal cavities as laid down 

 in pre-cartilage are much more complete (fig. 9, A) as shown by 

 examination of the sections, in which septum and side walls can 



