The brain of Acipenser. 93 
describe these in more detail. The long slender body usually bears 
an enlargement at one end from which the large dendrites diverge 
The nucleus may be in this enlargement or in another nearer the 
middle of the cell. The end of the cell body opposite the dendrites 
is drawn out to a slender point and becomes continuous with the 
neurite, which is thus always thick at its base and grows more 
slender as it leaves the cell. The cell body is frequently very ir- 
regular and crooked. One or more smaller dendrites usually arise 
from the side of the cell body. In measuring these cells I have 
taken the greatest thickness, which is often twice the average thick- 
ness. Consequently the PuRKINJE cells differ much less in volume 
than the measurements above given would indicate. The dendrites 
are very large, spread widely in the molecular layer and are pro- 
vided with the small spines which give them their characteristic 
appearance. The neurites of the PuRKINJE cells are difficult to 
trace to any distance from the cells. In the body of the cerebellum 
I have always found them running in the molecular layer in the 
same direction as the neurites from the granule cells. The PURKINJE 
neurites rapidly decrease in calibre until they are with difficulty 
distinguished from the neurites of the granules. I have not found 
any going into the granular layer. 
The ground substance of the molecular layer consists of fine 
fibres chiefly from the granular layer which are passing toward the 
dorsal surface to run in the molecular layer of the lateral lobe of 
that side to which their cells of origin belong. Toward the cephalic 
end of the body, where the structure resembles more and more that 
of the valvula, there are a few of the second variety of the cells of 
the II type described below. 
2. The Valvula. 
In the valvula the molecular and granular layers are so poorly 
defined that I shall describe the several elements in succession 
without reference to distinct layers. 
The granule cells of the valvula measure 8—12 by 9—14 u, 
and have the same appearance as those of the body. They send 
their neurites at first cephalo-mesad or ventro-mesad toward the 
keel of the valvula, where they turn to run dorso-caudad into the 
molecular layer of the lateral lobes. These neurites give off one 
or two, and in some cases several collaterals in the granular layer 
