THE CEKEBKO-SPINAL NERVOUS SYSTEM. 525 



Structure. The cerebellum is composed of white and gray matter, 

 the latter being external, like that of the cerebrum, and like it. infolded, 

 so that a larger area may be contained in a given space. The convolu- 

 tions of the gray matter, however, are arranged after a different pattern as 

 shown in Fig. 362. Besides the gray substance on the surface, there is, 

 near the centre of the white substance of each hemisphere, a small cap- 

 sule of gray matter called the corpus dentatum (Fig. 363, cd), resembling 

 very closely the corpus dentatum of the olivary body of the medulla ob- 

 longata (Fig. 363, o). 



If a section be taken through the cortical portion of the cerebellum, 

 the following distinct layers can be seen (Fig. 364) by microscopic exami- 

 nation. 



(1.) Immediately beneath the pia mater (p m) is a. layer of considera- 

 ble thickness, which consists of a delicate connective tissue, in which are 

 scattered several spherical corpuscles like those of the granular layer of 

 the retina, and also an immense number of delicate fibres passing up 



FIG. 363. Outline sketch of a section of the cerebellum, showing the corpus dentatum. The 

 section has been carried through the left lateral part of the pons, so as to divide the superior pe- 

 duncle and pass nearly through the middle of the left cerebellar hemisphere. The olivary body has 

 also been divided longitudinally so as to expose in section its corpus dentatum. c r, crus cerebri; 

 /, fillet; g, corpora quadrigemina; sp, superior peduncle of the cerebellum divided; m jo, middle pe- 

 duncle or lateral part of the pons Varolii, with fibres passing from it into the white stem; a v, con- 

 tinuation of the white stem radiating towards the arbor vitse of the folia; c d, corpus dentatum; o, 

 olivary body with its corpus dentatum; p, anterior pyramid. (Allen Thomson.) %. 



towards the free surface and branching as they go. These fibres are the 

 processes of the cells of Purkinje. (2.) The Cells of Purkinje (p). 

 These are a single layer of branched nerve-cells, which give off a single 

 unbranched process downwards, and numerous processes up into the ex- 

 ternal layer, some of which become continuous with the scattered cor- 

 puscles. (3.) The granular layer (g), consisting of immense numbers 

 of corpuscles closely resembling those of the nuclear layers of the retina. 

 (4.) Nerve-filre layer (/). Bundles of nerve-fibres forming the white 

 matter of the cerebellum, which, from its branched appearance has been 

 named the " arbor vitae." 



Functions. The physiology of the Cerebellum may be considered in 

 its relation to sensation, voluntary motion, and the instincts or higher 

 faculties of the mind. Its supposed functions, like those of every other 



