No. I.] THE CRANIAL NERVES OF AMPHIBIA. 1 55 



hereafter, some portions of the medulla oblongata undergo 

 remarkable variations in size and development in the different 

 types and in this respect the tract under consideration seems 

 to stand in contrast. This is natural when it is considered 

 that it forms the supply to the skin exclusive of the specialized 

 cutaneous sense organs which are peculiar to certain types 

 only, or, at least, in certain types obtain a much greater 

 relative development. 



Respecting the nature of this component there can be no 

 question, I think, that it is similar (homodynamous) to the 

 dorsal spinal roots, if internal origin, character of fibres and 

 their distribution are criteria of any weight. Its fibres are 

 a direct continuation of those in the posterior columns of the 

 cord, which they resemble, and are distributed to the skin 

 exclusive of any differentiations in the latter which belong 

 especially to the branchial region. This is also Gaskell's view 

 (23 and 24). 



It follows from this that the sensory Trigeminus is largely 

 equivalent to the dorsal spinal roots, minus, possibly, their 

 splanchnic fibres. Besides the Trigeminus, however, the same 

 component is represented in the vago-glossopharyngeal group, 

 and that to a greater extent than is commonly supposed. The 

 homology of what is here denominated the R. auricularis vagi 

 has already been touched upon. The branches, or branch, 

 which Stannius and others have homologized with the R. 

 auricularis vagi in higher forms, appear to be the supratemporal 

 branches to lateral-line organs. There is every reason to sup- 

 pose, however, that the lateral-line system of nerves completely 

 disappears in the higher forms, especially as the root which 

 supplies them disappears. One of these supratemporal branches 

 in the tadpole is described above. Consequently the homologue 

 of the R. auricularis vagi in higher forms must be the branch 

 in the tadpole which I have described above as the R. auricu- 

 laris, which has no connection with the lateral-line system 

 and belongs to the general cutaneous system. The question 

 arises, then, as to what is the homologue in lower forms of the 

 R. auricularis vagi of the tadpole. I may here simply say that 

 I believe that future investigation will bring out more clearly a 



