210 Journal of Comparative Neurology and Psychology. 



the more primitive forms, and the place of ending of its ascend- 

 ing fibers in fishes and amphibia the writer has assigned N. V 

 to the cerebellar neuroraere, vi. 



In connection with the ganglia of the profundus and 

 trigeminus are dorsal-lateral placodes giving rise to cells whose 

 fibers form the Rr. ophthalmicus superficialis and buccalis of 

 the facialis. These are of great importance for the interpreta- 

 tion of the lateral line components and their relation to the 

 general cutaneous system. They will be referred to again (Sec. 

 lO). 



The exit of the trochlearis from the dorsal surlace of the 

 brain and its decussating at that point is a puzzle for which no 

 adequate solution has yet been offered. The writer has only a 

 brief suggestion to make. The course of the root fibers dor- 

 sally through the brain wall may be due to the course of the 

 fiber tracts among which they run. The position of the nucleus 

 of the nerve relative to the tracts which form the ansulate com- 

 missure in typical fishes suggests strongly that the axones from 

 the cells of the trochlearis nucleus may have followed some of 

 these bundles as the path of least resistance. The tracts be- 

 tween the tectum opticum and the base of the oblongata, the 

 tracts between the inferior lobes and the cerebellum, and others, 

 all running more or less dorso-ventrally in the side wall of the 

 brain and decussating ventrally at the level of the trochlearis 

 nucleus — these bundles, which lie ectal to the nucleus of the 

 trochlearis, may have constituted an effective barrier to the 

 axones of the trochlearis iij their attempt to reach the ventro- 

 lateral surface of the brain. The axones may then have turned 

 upward along the ental surface of these bundles until they reached 

 the dorsal surface of the brain. If the fibers were thus directed 

 in their course they would be carried to the mid-dorsal line be- 

 fore gaining an exit from the brain and if they then grew 

 straight on they would pass to the opposite side. In Acipenser 

 {6y, p. 139) the root fibers are so intimately wrapped up in a 

 heavily medullated bundle which rises from the region of the 

 nucleus of IV to the dorsal surface of the cerebellum that it is 

 easy to imagine the course of the root being determined by the 



