34 ATLAS OF NERVE CELLS 



THE CEREBELLAR CORTEX 



THE cortex of the cerebellum is, by reason of its numerous fine convolutions, almost as 

 extensive in area as that of the cerebrum. It is made up of two distinct layers of gray 

 matter, between which lie the large Purkinje cells, which form the chief characteristic of this 

 organ. Everywhere beneath these layers of gray matter the nerve fibres collect into white 

 masses, which pass in various directions, bringing the cerebellum into relation with other parts 

 of the nervous system. 



Plate XIV. shows the existence of the two cortical layers, and the appearance of the 

 Purkinje cells (P) l in the adult human brain. 



The first, or superficial, layer of the cortex has been named the molecular layer. 



The second, or deep, layer of the cortex is known as the granular layer. 



The Purkinje cell body lies between these layers, and its dendrites pass into the super- 

 ficial layer, while its neuraxon passes into the deep layer. 



The body of the Purkinje cell " is round or oval, as shown in Plates XIV. and XV. 

 There are several large protoplasmic extensions of the body which give off numerous branches 

 soon after leaving the body, and these branches present the extraordinarily rich sub-branching 

 which is peculiar to the Purkinje cell. It will be noticed that all these dendritic branches 

 have a rough surface. This is owing to the presence of fine thorn-like excrescences close 

 together on the branch. A high power of magnification shows that these excrescences have 

 clubbed extremities, not being pointed as thorns are. The excrescences have been called 

 gemmules. This extraordinary mass of branches of the Purkinje cell has been termed its 

 arborization. But their arrangement is not exactly like that of a tree, for it is found that 

 these branches all lie in one plane, a plane transverse to the folding of the convolution. 

 Hence if the convolution is cut in a longitudinal plane, the cells and branches are seen only 

 as a thin vertical line. The natural position of the branches may then be compared to the 

 artificial position given to the branches of a plant which has been pressed in a herbarium. 

 As the vast majority of the fine nerve fibres of the molecular layer of the cerebellum have 

 a horizontal and longitudinal direction, it is evident that they can pass through and between 



1 These letters refer to Figure 6. on page 39. 



