22 Journal of Comparative Neurology. 



I have been unable to trace their neurites, I have no doubt that 

 they are the granule cells and that the fine fibers of the molec- 

 ular layer and cerebellar crest are derived from them. 



The fibers which enter the cerebellum have been partly 

 described. The VIII fibers are dichotomous branches of the 

 root fibers and are relatively fine. They run along the outer 

 surface of the acusticum nuclei or through the dorsal nucleus 

 and through the inner part of the molecular layer of the cere- 

 bellum. They do not end in this layer but bend inward to- 

 break up in the granular layer. The lateral VII fibers are very 

 coarse, run deeper in the cerebellum and enter the granular 

 layer directly. No part of them is ever seen in the molecular 

 layer. The relatively small number of V fibers entering the 

 cerebellum are mingled with the VIII and lateral line fibers so 

 that their course can not be separately traced. In addition tO' 

 the above, a part of the tract from the lobus inferior, tractus 

 lobo-cerebellaris, ends in the cerebellum. 



From this description of the minute structue of the cuta- 

 neous centers the following conclusions may be drawn in addi- 

 tion to those noted above : 



(i) The cell elements or neurones in the nucleus funiculi^ 

 acusticum (excepting the spindle cells), and cerebellum are ap- 

 parently identical. 



(a) Large cells with well developed dendrites and with 

 neurites which become internal arcuate fibers. These are to be 

 regarded as the primitive cells from which Purkinje cells have 

 developed in the cerebellum and acusticum of selachians and 

 ganoids and in the cerebellum of other vertebrates. 



(b) Small cells homologous with the granule cells of the 

 cerebellum of higher vertebrates and similar to the granule cells 

 found in the acusticum of Acipenser. 



(c) Cells of the II type have not been found in any of 

 these nuclei in Petromyzon. 



(2) There is actual continuity of tissue between all these 

 centers, and the fibers of the VIII nerve probably end in all 

 of them. The fibers of the lateral line VII end in the acusti- 

 cum and cerebellum, and those of the V end in the nucleus 



