1 94 STRONG. [Vol. X. 



belongs to the general cutaneous system (Ahlborn, Gorono- 

 witsch, Ewart). 



I may add, in support of Wilder' s view, the relation of the 

 R. ophthalmicus trigemini, in the tadpole, to the III and IV 

 nerves. It lies in the fork formed by the division of the III 

 into its inferior and superior branches, and likewise comes into 

 relation with the IV. In Galeus canis the R. ophthalmicus 

 profundus bears precisely the same relation to the III while the 

 R. ophthalmicus superficialis V bears the same relation with 

 the IV that the single R. ophthalmicus trigemini bears to these 

 two nerves in the tadpole. 



As far as I can ascertain, the root from the lobus trigemini 

 is probably coarse-fibred in Selachians. As the roots from the 

 tuberculum acusticum are devoted to the canals, it would seem 

 likely that those fibres in the lateral line nerves of the head 

 derived from the lobus trigemini are devoted to the innervation 

 of the ampullae. If this were true, as further research is nec- 

 essary to show, the ampullae would represent the end buds of 

 other fishes. The absence of a R. lateralis from the lobus tri- 

 gemini in Selachians and the concomitant absence of such 

 organs on the trunk is significant in this connection. 



The innervation of the pit organs should be studied in this 

 connection. If innervated by fibres from the lobus trigemini, 

 it would appear that they have been secondarily specialized 

 from the end buds and added to the lateral line system. 



If it is true, furthermore, that the fine-fibred root from the 

 lobus trigemini in Teleosts and Ganoids is represented by a 

 coarse-fibred root in Selachians, we have a most interesting 

 case bearing upon the significance of fibre-calibre. Here the 

 principal change, apparently, in the structure innervated is a 

 sinking below the surface and a probable increase in size. 



As has been seen, there seems to be no lobus trigemini in 

 Amphibia. This is not difficult to understand now when it is 

 considered that the end buds are confined to the mouth in 

 Amphibia, and, consequently, much reduced in number. The 

 Trigeminus, however, as described by Osborn, derives its fibres 

 internally from the following sources : (i) The ascending 

 tract from the cervical region, reinforced by (2) fibres from the 



