CH. XLV.j THE CEREBELLUM 649 



matter ;has given rise to the name arbor vitce. Besides the grey 

 substance on the surface, there are, in the centre of the white sub- 

 stance of each hemisphere, small masses of grey matter, the largest of 

 which, called the corpus dentatum (fig. 471, cd), resembles very closely 

 the corpus dentatum of the olivary body of the medulla oblongata in 

 appearance. 



If a section is taken through the cortical portion of the cere- 

 bellum, the following distinct layers can be seen (fig. 472) by micro- 

 scopic examination. 



Underneath the pia mater is the external layer of grey matter ; it 

 is formed chiefly of fine nerve-fibres with small nerve-cells scattered 

 through it. Into its outer part, processes of pia mater pass verti- 

 cally; these convey blood-vessels. There are also here numerous 

 long tapering neuroglia-cells. The internal or granular layer of grey 



FIG. 471. 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 peduncle and 

 pass nearly through the middle of the left cerebellar hemisphere. The olivary body lias also been 

 divided longitudinally so as to expose in section its corpus dentatum. cr, crus cerebri ; /, fillet ; q, 

 corpora quadrigemina ; s p, superior peduncle of the cerebellum divided ; m p, middle peduncle or 

 lateral part of the pons Varolii, with libres passing from it into the white stem ; a v, continuation 

 of the white stem radiating towards the arbor vit<e of the folia ; c d, corpus dentatum ; o, olivary 

 body with its corpus dentatum ; p, pyramid. (Allen Thomson.) H. 



matter is made up of a large number of small nerve-cells mixed with 

 a few larger ones, and some neuroglia-cells. Between the two layers 

 is an incomplete stratum of large flask-shaped cells, called the cells of 

 Purkinje. Each of these gives off from its base a fine process which 

 becomes the axis-cylinder of one of the medullated fibres of the white 

 matter ; the neck of the flask passing in the opposite direction breaks 

 up into dendrites which pass into the external layer of grey matter. 

 By Golgi's method (fig. 473) these dendrons have been shown to 

 spread out in planes transverse to the direction of the lamellae of the 

 organ. 



Each cell of Purkinje is further invested by arborisations of two 

 sets of nerve-fibres. One of these (originating from the fibres of the 

 white matter which are not continuous as axis-cylinders from the 

 cells of Purkinje) forms a basket-work round the dendrons ; the other 

 originating as axis-cylinder processes from the nerve-cells of the 



