Terry — The Nasal Skeleton of Aviblystoma punctattim. 115 



Amblystoma. This roof cartilage then arises in connection 

 with what was originally ethmoidal column and Crista trahe- 

 culae. Subsequently it spreads over the caudal end of the 

 nasal sac to fuse with the antorbital process, leaving a pas- 

 sage way for the Ramus nasalis trigemini. 



The early relations and form, and the later secondary 

 connections and development of the ethmoidal column of 

 Rana are the same as obtained for the rod (Col. eth.) in 

 Amblystoma and even the origins of the two are not essen- 

 tiallv different: the one growing in connection with the 

 anterior trabecular plate (itself a development of the trabe- 

 cula), the other chondrifying in a mass of cells streaming up 

 from the end of the trabecula at the spot where the trabecular 

 plate is growing. 



The nasal skeleton in Necturus and in Proteus remains 

 unconnected with the brain-case throughout life and in both 

 consists of a lattice-work of cartilage as described by Wie- 

 dersheim ('77 and '02 Fig. 200) and Wilder ('03). In Nec- 

 turus this incomplete capsule covers the simple nasal sac dor- 

 sally and in part medially ; also to a considerable extent at 

 the poles. 



My own studies have shown that the position of the nasal 

 sac of Necturus is laterad of the brain in young animals and 

 latero-cephalad in older ones, the bony wall of the cranium in- 

 tervening and the branches of the olfactory nerve running an 

 extra-cranial course to the nasal sac. 



Miss Piatt ('97) and Winslow ('98) have described the 

 independent origin of the nasal skeleton in Necturus and 

 in the work of the former writer we learn that the inter- 

 nasal ( anterior trabecular ) plate and the dorsal part of the 

 Crista trabeculae chondrify independently. The latter is 

 never high in Necturus as it is in Amblystoma and Rana and 

 its cephalic ending is gradual, not abrupt. In the 45mm. 

 larva described by Winslow a curved bar of cartilage appears 

 on the dorso-mesal surface of the olfactory organ running 

 about parallel with the anterior end of the trabecula, dorsad 

 of which it lies. From this bar a number of shorter processes 

 extend laterally over the nasal sac and there are also some sep- 



