No. I.] THE CRANIAL NERVES OF AMPHIBIA. 195 



deep motor nucleus, representing two tracts. (3) Fibres from 

 the sensory nucleus. (4) The descending tract from the mes- 

 encephalic nucleus. (5) The direct encephalic tract. . . . 

 ''The sensory nucleus is very large and extends forwards 

 beyond the level of the cerebellum." It is possible this sensory 

 nucleus is representative, partly, of the lobus trigemini. 



In any case, the disappearance of this system of nerves as a 

 separate system in Amphibia in correlation with the dis- 

 appearance of these cutaneous organs is a most interesting 

 phenomenon. In the Amphibia, then, we have a reduction 

 already accomplished in the disappearance of the end bud 

 nerves, and in the Anura another reduction in process of 

 accomplishment in the loss of the lateral line nerves, in several 

 forms at least, as the fully developed anurous condition is 

 attained. 



These questions all have an intimate bearing upon the origin 

 of taste and upon the vexed question of the innervation of the 

 taste buds in the higher vertebrates. It is easily seen that the 

 problem is one of extreme complexity. It is not unreasonable 

 to expect, however, that thorough comparative researches upon 

 the exact composition of the cranial nerves will clear up these 

 obscure points. 



Stated briefly, we seem to have the following alternatives : 

 {a) The taste buds (end buds) are innervated in the lower 

 forms by the root from the lobus trigemini only. As the latter 

 diminishes, owing to the loss of the end buds on the exterior, 

 these fibres fuse with the Trigeminus proper. This view does 

 not seem to harmonize well with the facts in Amphibia, as stated 

 above, namely, the innervation of end buds by the R. mandi- 

 bularis internus VII, R. lingualis IX, etc. The R. palatinus, 

 and even the R. mandibularis internus VII, might indeed 

 receive the fibres in question through the anastomoses with 

 the V. This would tend to show that the V is the nerve of 

 taste in the higher forms. 



(b) The innervation of these structures can be regarded as 

 shifted from one set of nerves to another, i.e.^ from those 

 issuing from the lobus trigemini as this diminishes or is lost, 

 to those issuing from the lobus vagi (fasciculus communis). 



