296 ILLINOIS ACADEMY OF SCIENCE 



the lamina externa, is likewise continuous with the an- 

 terior end of the pterygoquadrate. 



In Cryptobranehus, then, these relationships between 

 the pterygoid and the nasal capsule, as found in the 

 Anura, are carried over into the Urodela; and it would 

 seem that the antorbital process, the pterygoid and the 

 planum tectale of the Urodela may be readily homolo- 

 gized with these structures in the Anura. That being 

 true, it would apparently follow that the antorbital pro- 

 cess in Cryptobranehus and perhaps in all Urodeles, is, 

 at least in its basal part, derived from the anterior part 

 of the pterygoquadrate arch ; while the more distal por- 

 tion which must be the homologue of the lamina externa 

 of the Anura, may be a new formation. It may be re- 

 marked, that in both the Anura and the Urodeles, the 

 antorbital process unites with the cornu trabeculae, a 

 structure clearly homologous throughout the class 

 Amphibia, thus furnishing a further clue to its relation- 

 ships. 



In the early stages of the chondrocranium of Salaman- 

 dra maculata, a Urodele in which the pterygoquadrate 

 does not reach forward into the nasal region, the antor- 

 bital process arises from the trabecula much as in Am- 

 blystoma. During its development, the planum tectale, 

 which forms the roof of the nasal capsule, develops lat- 

 erally from the posterior end of the columna ethmoidalis ; 

 and, curving ventrally, covers the posterior and lateral 

 parts of the nasal organ. In a larva, 38 mm. long, the 

 anterior end of the distal part of the antorbital, which 

 has developed forward toward the capsule, has come to 

 lie just beneath and slightly posterior to the lateral mar- 

 gin of the planum tectale; so that these two structures 

 are separated by a wide gap, through which the ophthal- 

 micus and the superficialis branches of the fifth nerve 

 pass to the nasal organ. Thus the antorbital process is 

 ventral to these nerves. In all Urodeles, with the excep- 

 tion of Necturus and Amphiuma, in which the antorbital 

 process does not unite to the structures farther forward, 

 and probably in the later stages of Salamandra, this 

 wide gap is reduced to an orbito-nasal foramen, which 



