CoGHiLL, Cranial Nerves of Amblystoina. 253 



PART SECOND. 



A COMPARATIVE DISCUSSION OF THE CRANIAL NERVES OF 



AMBLYSTOMA. 



I. The Olfactory Nerve. 



Stieda ('75) and Herkick ('94) consider that the olfactory 

 nerve of Amblystoma arises by a single root. Nor do they 

 mention any particular division of the nerve to Jacobson's 

 organ. Seydel ('95), however, has observed the peculiar 

 branch of the nerve to this organ in larval Amblystoma, though 

 he argues that this branching of the olfactory nerve has no 

 morphological significance. 



Before criticizing Seydel's conclusion, one should review 

 a few facts concerning the olfactory nerve of Amphibia. In 

 Gymnophiona and Triton (Burckhardt, '91), Cryptobranchus 

 (McGregor, '96), Diemyctylus (Gage, '93), and in Anura there 

 occurs a greater or less separation of the olfactory nerve into two 

 divisions from the origin of the nerve towards the periphery. 

 In Gymnophiona and Triton these two divisions are distinct 

 throughout the entire extent of the nerve, and the more ven- 

 tral of the two innervates Jacobson's organ. Also in Amphi- 

 uma (Kingsley, '92) and in Diemyctylus (Gage, '93) and in 

 some other Amphibia there is a particular branch of the nerve, 

 the exact central relation of which is not known, which inner- 

 vates Jacobson's organ. These facts, especially in view of the 

 clear relations in Gymnophiona and Triton, indicate that there 

 are two morphologically distinct elements in the olfactory nerve 

 of Amphibia. 



In the full light, however, of the facts as they appear in 

 Gymnophiona and Triton, Seydel concludes that the particular 

 branch of the nerve which innervates Jacobson's organ has no 

 morphological value. He bases this conclusion, largely or 

 wholly, upon the fact that this branch gives fibers, also, to the 

 olfactory epithelium proper. My own observations show that 

 such an interchange of fibers might take place between the two 

 elements- of the nerve. However, this fact seems to me of 



