4 o ATLAS OF NERVE CELLS 



plate also shows the large number of horizontal fibres in the molecular layer. The granular 

 layer is made up almost completely of these cells, which are very numerous, lying closely 

 packed together. 



Among them are other cells of larger size, first described by Golgi, multipolar, with many 

 dendrites and a neuraxon, which divides and subdivides soon after leaving the cell, forming 

 an extensive plexus through the molecular layer (ff). These cells belong to Golgi's second 

 type of cell. They are not shown in the plate, but are figured in the diagram (Fig. 6, //). 

 The dendrites of these cells enter the molecular layer, but their neuraxon, with its numerous 

 subdivisions, lies in the granular layer. 



The mutual arrangement of the various cells of the cerebellum may best be understood 

 by the aid of the diagram (Fig. 6). 



The termination of fibres entering the cerebellum in the granular and molecular layers 

 has been investigated by Cajal. He describes in the granular layer a number of branching 

 fibres with short, divergent extremities which have a particularly thick appearance with furry 

 surface, and these he has called the moss-like fibres, since their appearance under the micro- 

 scope resembles a collection of moss-stems (M). This appearance was thought at first to be 

 an artifact, but Van Gehuchten and Retzius have confirmed their existence. This moss-like 

 terminal structure is confined to the granular layer, and seems to bring the impulses coming 

 into the cerebellum through these fibres into relation with the small polygonal cells of this 

 layer. 



The termination of fibres entering the molecular layer of the cerebellum is different from 

 that seen in the granular layer. These fibres, after entering the molecular layer, appear to 

 branch very much in the same manner as the cells of Purkinje branch, and the branches of 

 these fibres run parallel with and quite near to the branches of the Purkinje cells, so that 

 there appears to be a second arborization in this layer, enabling the impulses reaching this 

 layer to pass into the Purkinje cell. 1 Cajal has compared this arrangement to that of ivy 

 climbing up a tree, the Purkinje cell being the tree, and these branches the ivy. 



1 KSlliker does not agree with this view, but thinks the branches are less complex than those of the Purkinje cells and that 

 these fibres come rather into contact with the basket cells. 



