320 ANATOMY OF THE CENTRAL NEEVOUS SYSTEM. 



Eecall that in Chapter III it was stated that according to recent views 

 the connection of one cell to another, in the central nervous system, is 

 established through the protoplasmic processes of one cell being surrounded 

 by the terminal ramifications of the neuraxons of the other. Since the term 

 neuron includes the cell and its protoplasmic processes with the neuraxon 

 and its terminal ramification, one may say: In the whole nervous system 

 there are innumerable separate neurons which are associated together in the 

 manner described above. An example of this is also found in the olfactory 

 lobe. In the minute structure of the cerebellum we may verify the prin- 

 ciple just formulated. 



The cells of Purkinje (see 1 in Fig. 307) send neuraxons down into the 

 zona granulosa and into the medullary layer below this. On the way they 

 give off collaterals, some of which bend around, pass upward, and break up 

 into branches around the body of the cell. The dendritic processes are 

 extraordinarily profiTse, especially in the sagittal plane, — less so in the 

 transverse plane. If one wishes to get such a view as is shown in Fig. 807, 

 the sections must be cut transverse to the fissures of the cerebellum. 



The profuse dendritic branches are now interspersed with thick fibers 

 (see 2, Fig. 207), which, coming from cells of unknown location, enter the 

 cerebellar medulla, traverse the zona granulosa, finally breaking wp into 

 branches in the zona moleeularis. Thus, every cell of Purkinje is placed 

 in connection with a distinct locality. But there is a kind of cell in the 

 molecular layer which is adapted to bring into connection with each other 

 a number of the Purkinje cells. Such cells (see 3, Fig. 207) send out, nearly 

 parallel to the surface of the cortex, a long neuraxon, which gives out fine 

 processes at intervals along its course. A process passes to the body of one 

 of the Purkinje cells, and breaks up into branches around it. 



The granular layer consists, for the most part, of small polygonal cells 

 with large nuclei (see 4, Fig. 207). Each one of these cells sends out a 

 number of short dendrites and a neuraxon. The latter passes outward into 

 the molecular layer, where it divides into two fibers which are transverse to 

 the axis of the body. In the figure this division is indicated by a short trans- 

 verse line because the section is a sagittal one, — i.e., transverse to the con- 

 volutions of the cerebellum. The numerous dots scattered over the molecu- 

 lar layer in the lower right hand part of the figure represent the sections of 

 these neuraxons. Besides the cells just described, there are, in the granular 

 layer, cells whose neuraxons break up at once into very fine twigs which 

 ramify among the elements of the granular layer and whose dendrites — not 

 unlike those of the Purkinje cells, though less branched — are distributed to 

 the molecular layer. Furthermore, there end in the granular layer fibers of 

 unknown origin which enter this layer, from the medullary layer (see 6. 

 Fig. 207). 



