i6 Journal of Comparative Neurology. 



with the granular layer of the cerebellum and that there is a 

 well-defined prolongation of the molecular layer backward over 

 the acusticum. This is homologous with the cerebellar crest of 

 Acipenser and selachians. 



4. That there is a distinct nucleus lying dorsal to the 

 acusticum proper and partly separated from it by the cerebellar 

 crest, which receives the fibers of part of the lateral line VII 

 nerve. This nucleus is homologous with the lobus lineae later- 

 alis (so-called lobus trigemini) of Acipenser and selachians. 



A careful examination of the elements of these several 

 nuclei and of the mode of ending of the sensory fibers in them 

 throws additional light on their relationship and their probable 

 history. 



1. Nucleus funiculi (Figs. 6-9, d. h. and n. f.y 



The spinal V tract enters the nucleus at its ventral border 

 and the fibers take a dorso-caudal course, so that they are cut 

 very obliquely in transverse sections. In the middle and ceph- 

 alic part of the nucleus these fibers form a dense mass, being 

 more closely packed at the ventral angle, and between them 

 the cells lie scattered without any regular arrangement. The 

 character of the cells may be seen from the figures. The greater 

 number are large cells (10-24 X 16-50 />«) of various forms 

 whose dendrites are large and well branched. Their neurites go 

 as internal arcuate fibers across the ventral raphe. The small 

 cells (8— 10 X 10— 14/j!), are few in number and have short, 

 poorly branched dendrites. I have been unable to trace the 

 neurites of these cells to my satisfaction. 



2. Nucleus trigemini spinalis. 



The nucleus accompanying the spinal V tract is never 

 clearly impregnated in my preparations. When the cells are 

 impregnated there is so much precipitate fetween them that it 

 is impossible to give an accurate description of the larger cells. 

 They have the same appearance in haematoxyhn sections as 

 those of the nucleus funiculi. In a few cases smaller cells 

 (8-10 X io-i2/y.) were found, and these closely resemble the 

 smaller cells of the nucleus funiculi and acusticum. 



