386 ROBERT J. TERRY 



lamina infracribrosa is a part of the antorbital division of the nasal 

 capsule, entering into the floor of the cranium. The course of 

 the ethmoidal nerve is, strictly speaking, outside the chondro- 

 cranial cavity, since the layer of mesenchyma (probably in part 

 giving rise to dura), which covers the lamina infracribrosa, stands 

 between it and the cerebral cavity. In the cat, in the stages 

 studied, there is no overhanging anterior wall of the chondrocran- 

 ium such as is shown in the model of Echidna; a flat anterior 

 margin of the fenestra olfactoria marks the anterior limit of the 

 cranial cavity. Consequently, the term 'recessus' supracribro- 

 sus is hardly appropriate for the cat; the term 'supracribrous 

 region' is preferable. From these data, it seems that the eth- 

 moidal region of the cat, like the orbito-temporal and otic re- 

 gions, gives evidence in support of Gaupp's assertion of the non- 

 equivalency of reptilian and mammalian crania, and also, by its 

 relations to the chondrocranial cavity, indicates that the latter 

 is enlarged over that of reptiles by the acquisition of a region 

 wholly extracranial in that class. A factor having a large share 

 in bringing about this mammalian characteristic is the backward 

 growth of the nasal cavity (Weber, '04; Gaupp, '08) whereby the 

 interorbital septum is encroached upon by the posterior cupola 

 of the ethmoidal skeleton. That this occurs to a slight extent 

 in the ontogeny of the cat was indicated by the difference in posi- 

 tion of the posterior cupola relative to the preoptic process in 

 earlier and later embryonic stages. 



In Lepus, according to Voit, the foramina of the lamina cri- 

 brosa are separated into two groups by a crista intercribrosa, ol- 

 factory filaments from the recessus lateralis traversing the foram- 

 ina of the antero-lateral group, those from the recessus posterior 

 (ethmoturbinal region) passing through the holes of the postero- 

 medial group. Voit also found the- dorsal end of ethmoturbinal 

 I continuous with the crista intercribrosa. Continuity between 

 these two parts is present in Caluromys philander, as observed 

 by Dr. Denison in ' this laboratory. In the cat, at the stage 

 modeled, the dorsal end of ethmoturbinal I is very prominent 

 and stands between the group of olfactory filaments coming from 

 the epithelium of the recessus lateralis and those from the ethmo- 



