CH. XLVII.] THE CEREBELLUM 681 



matter on section has given rise to the name arbor vitce. Besides 

 the grey substance on the surface, there are, in the centre of the 

 white substance of each hemisphere, small masses of grey matter, the 

 largest of which, called the corpus dentatum (fig. 420, cd), resembles 

 very closely the corpus dentatum of the olivary body in appearance. 



FIG. 420. 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 has also been 

 divided longitiidinally so as to expose in section its corpus dentatum. cr, Crus cerebri ; /, tillet ; q, 

 corpora quadrigemina ; sp, superior peduncle of the cerebellum divided ; mp, middle peduncle or 

 lateral part of the pons Varolii, with fibres passing from it into the white stem ;%w, continuation 

 of the white stem radiating towards the arbor vitai of the folia ; cd, corpus dentatum ; o, olivary 

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



In a section through the cerebellar cortex the following layers 

 can be seen. 



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 

 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 process which 

 becomes the axon 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. 421) 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 

 external layer) forms a felt-work of fibrils round the body of the 

 cell. 



The cells of the internal layer of grey matter are small ; their 



