STRUCTURE AND FUNCTIONS OF THE CEREBELLUM. 



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380. STRUCTURE AND FUNCTIONS OF THE CEREBELLUM. [Structure. On examin- 

 ing a vertical section of a cerebellar leaflet, we observe the following microscopic appearances : 

 Externally, is the pia mater with its blood-vessels (fig. 506, a), which penetrate into the 

 grey matter ; within is the medulla, composed of white fibres. The grey matter consists of b, 

 a broad outer or molecular layer, largely composed of branched fibrils ; and internal to it is d, 

 the " granular," nuclear, or rust-coloured layer. On the boundary line between these two, is 

 the layer of Purkinje's cells, c. The cells of Purkinje form a single layer of large multipolar 



flask-shaped nerve-cells, which have been 

 compared to the branched antlers of a stag 

 (fig. 507). From their outer surface is given 

 off a process which rapidly divides, and gives 

 rise to a large number of smaller processes 

 running outwards in the outer grey layer. 

 Some of these processes form part of the 

 ground-plexus of fibrils in this layer. An 

 unbranched axial cylinder process is sent 

 inwards to the granular layers, where it be- 

 comes continuous with a nerve-fibre every 

 cell of Purkinje being continuous with a 

 straight unbranched medullated nerve-fibre. 

 The unbranched fibres run straight from the 

 medulla through the granular layer, forming 

 no connection with its granules. A second 

 set of branched or anastomosing, often vari- 

 cose, nerve-fibres, finer than the foregoing, 

 pass from the medulla into the granular 

 layer, where they form a network which is 



Fig. 506. Fig. 507. 



Fig. 506. Vertical section of the cerebellum, a, pia mater; b, external layer ; c, layer of 



Purkinje's cells ; d, inner layer ; e, medullary white matter. Fig. 507. Purkinje's cell, 

 sublimate preparation, x 120. 



continued into the molecular layer. The granular layer is composed of closely packed 

 granules of two kinds ; one is stained by hematoxylin, and the other with eosin (Denissenko). 

 The hematoxylin stained cells are most numerous ; they consist of a nucleus surrounded 

 by protoplasm, and are what were formerly called granules. The eosin-stained cells, which 

 are also stained by nigrosin (Beevor), are interposed in the course of medullated nerve- 

 fibres. The haematoxylin cells, called glia-cells by Beevor, have processes, and form a net- 

 work throughout the granular layer, which also extends into the molecular layer. This net- 

 work is regarded as the continuation of the modified myelin of the nerve-fibres, and it forms 

 a capsule for the cells of Purkinje. The molecular layer consists of a ground substance, com- 

 posed of a spongy network of fine fibrils, which seem to be of the nature of neuro-keratin, 

 strengthened here and there by stronger fibres. In the meshes lies a homogeneous substance. 



