14 Journal of Comparative Neurology. 



nately not been able to ascertain with perfect certainty the 

 further course of those fibers. Only this much is certain, that 

 they turn in a horizontal direction along the boundary between 

 the granular and molecular layers and proceed a distance further 

 here in the form of isolated bundles. The roundish cross- 

 sections of these fiber-bundles which I have met with lying at 

 certain intervals from each other between the molecular and 

 granular layers demonstrate this sufficiently. I conjecture that 

 these fiber-bundles now gradually lose their individuality and 

 finally go over into the thick nervous plexus which we saw 

 locally so greatly developed beneath the Purkinje cells in other 

 regions of the cerebellar cortex. I further conjecture that 

 these bundles contain both centrifugal and centripetal fibers, 

 i. e. both the axis-cylinders of Purkinje cells and "ascending 

 fibers," or, in other words, all those tracts which, by means 

 of the crura cerebelli, furnish the functional communications of 

 the cerebellum with the other portions of the central nervous 

 system. 



Concerning the fibers of the molecular layers, here the as- 

 cending axis-cylinders of the small granule cells and their hori- 

 zontal branches are especially prominent. The former form 

 locally a dense forest, especially in those parts of the cerebellar 

 plate where the Purkinje cells are lacking (Plate II, fig. ii). 

 The axis-cylinders, as mentioned before, here increase some- 

 what in thickness and are quite thickly beset with varicosities. 

 The nervous processes of the "cortical cells" also participate 

 in the tangle of fibers in the molecular layer and likewise the 

 terminal arborizations of the "ascending fibers," of which I 

 have brought to view but little. 



I might mention here one peculiarity which all these fibers 

 appear to possess which pass from the granular into the molec- 

 ular layer and vice versa. This consists in the fact that all 

 these fibers in their passage from one layer to the other usually 

 undergo a double {bayonet shaped^ flexiite in that they bend for 

 a shorter or longer stretch into a horizontal direction, along this 

 intermediate zone, and then after a second bend, about at a 

 right angle, enter the other layer. The cause of the difficulty 



