134 ILLINOIS STATE ACADEMY OF SCIENCE 



involve planum basale, ethmoidal column, planum ethmoi- 

 dalis, the trabeculae and the cornua. 



In the adult the nasal organs are entirely separated 

 from each other as well as from cavum cranii by thick 

 cartilage walls, pierced only by foramina for the olfac- 

 tory nerves. Contrasting the two capsules, it is easy to 

 see that the median vertical plate, the planum verticale, 

 which separates the two nasal organs is but an anterior- 

 dorsal chondrification of the ethmoidal column along the 

 median line of the planum ethmoidalis. At the same time 

 it is evident further that the posterior wall of the nasal 

 capsule, separating the cavum nasi from the cavum 

 cranii, has arisen by a chondrification dorsally of the 

 planum basale, coupled with certain contributions from 

 the alisphenoids, in the transverse plane of the ethmoidal 

 column. In my single stage, although not mentioned in 

 the section describing the capsule, the olfactory nerve 

 passes anteriorly from the telencephalon through the 

 wide notch between the ethmoidal column and the alis- 

 phenoid cartilage (Fig. 8, OLF). Later, as chondrifica- 

 tion advances, cartilage layers form around this nerve, 

 so that in the adult the olfactory nerves are found to 

 pierce this posterior wall of the capsule, passing thence 

 to the various parts of the nasal organ. 



The floor of the nasal capsule of the older toad is 

 considerably larger than the planum ethmoidalis of this 

 stage, and it would appear that it has been formed by a 

 further fusion of the trabeculae forward to the region of 

 the cornua. No trabeculae as such are identified in the 

 older stage, and it follows that they have lost their iden- 

 tity in the formation of the complex anterior part of the 

 older capsule. The floor is wider than before so that a 

 large portion of the nasal organ now rests upon it, giving 

 it support, as well as additional protection. Anteriorly 

 the cornua trabeculae persist even into the adult stage, 

 where they take a more lateral direction and form what 

 are known as the alinasal cartilages which support the 

 anterior part of the nasal organ and form the floor of the 

 external naris. 



There remains for consideration the roof of the older 

 stage, and if we may accept the evidence of such types 



