a4 THE NERVOUS SYSTEM. q 
side of the mesial plane, and, although they appear to he within the cavity, they 
are in reality excluded from it by the epithelial lining of the ventricle, which covers 
over and is adapted to every sinuosity on their surface. 
Two lateral offshoots from these longitudinal choroid plexuses proceed outwards, 
and protrude in a similar manner into the lateral recesses. 
MINUTE STRUCTURE OF A CEREBELLAR FOLIUM. 
A cerebellar folium is composed of a central core of white matter, covered by a layer of - 
gray matter. The gray cortex is arranged in two very evident layers, viz. a superficial 
molecular layer and a subjacent rust-coloured granular layer. Between these strata a 
single layer of large cells, termed the cells of Purkinje, are disposed in the form of a 
very nearly continuous sheet. The cells of Purkinje constitute the most characteristic, 
and probably the most essential, constituents of the cerebellar cortex. 
The cells of Purkinje are most numerous on the summit of the folium, and at the 
bottom of the sulci which intervene between the folia they become fewer in number, and, 
therefore, looser in their arrangement. Each consists of a large flask-shaped or pyriform cell 
body, the narrow end of which projects into the molecular layer, whilst the thicker, 
deeper end rests on the granular layer. From the latter arises a single axon, which passes 
eee at keen into the granular layer and 
presents the peculiarity of 
almost immediately assum- 
ing its medullary sheath. 
From this axon a few col- 
lateral branches soon arise, 
which, taking a recurrent 
course, enter the molecular 
layer, to end in connexion 
with certain of the adjoin- 
ing cells of Purkinje. They 
would seem to have the 
function of binding together 
adjacent cells, and thus en- 
abling them to carry on 
their operations in harmony 
with each other. 
The dendritic processes 
spring from the narrow end 
of the cell either in the 
form of one or perhaps two 
stout stalks. These ascend 
into the molecular layer, 
branching and rebranching 
until anarborescent arrange- 
ment of extraordinary rich- 
ness and extent results. 
Fia. 352.—TRANSVERSE SECTION THROUGH A CEREBELLAR FOLIUM 
(after Kolliker), The dendritic branches ex- 
Treated by the Golgi method. tend throughout the entire 
BAND Pabeon of cellos Pantano! thickness of the molecular 
F. Moss fibres. layer, and the branching 
K and K?, Fibres from white core of folium ending in molecular layer in takes place in one plane 
: connexion with the USHHMSS of the cells of Purkinje. only, viz. in a plane which 
ae PERE ey the molecular layer. is transverse to the long axis 
GR.! Axons of granule cells in molecular layer cut transversely. of the folium. Consequently, 
M!.  Basket-cells. it is only when transverse 
ZK. Basket-work around the cells of Purkinje. sections are made through 
GL. Neuroglial cell. 
RUA U oe civ ascociationtell) a folium that the full den- 
dritic effect is obtained ; in 
sections made parallel to the long axis of the folium the cells are seen in profile and are 
observed to occupy quite a narrow area. The branching of the dendrites of a cell of 
Purkinje may, therefore, be compared to that which takes place in the case of a fruit-tree 
which is trained against a wall. 
In the molecular layer the cells are not particularly numerous, and of these the 
