78 J. B. JOHNSTON, 
contains fewer cells, and consists chiefly of fibres of the VIII and 
lateral line roots on their way to the cerebellum (Phots. 12—15). 
At the cephalic end of the medulla the acusticum becomes continuous 
with the body and lateral lobes of the cerebellum. I shall now 
describe in detail the elements entering into the structure of the 
tuberculum acusticum. 
Cells of the acusticum. — The most conspicuous of these 
are the large cells described and figured by GORONOWITSCH as 
PURKINJE cells. These are true PURKINJE cells which lie close 
beneath the cerebellar crest, in which their dendrites ramify (Phots. 37, 
38, and 45). They measure 8—32 by 32—336 u. In some cases 
there is a distinct cell body measuring 24 to 56 w in length, but 
usually the cells are so much elongated as to have no distinct cell 
body. In many cases it is impossible to give measurements of the 
cells because there is no limit between the cell body and the den- 
drites. One such cell with an extremely elongated and irregular 
form is shown in Phot. 38. Frequently the greatest mass of proto- 
plasm is at the base of the large dendrites (Phot. 37). These usually 
arise by a common thick stem from one end of the cell and divide 
and subdivide in the cerebellar crest. Each branch bears innumerable 
small spines which give to the dendrites their characteristic appearance. 
These spines are merely small pointed projections on the side of 
the dendrites and are of unequal length. The spines on the dendrites 
of cells in the tectum, inferior lobes, and epistriatum differ from 
these in being longer and bearing small rounded knobs at their 
ends. Compare Phots. 38, 41, 59, 75, and 79, which all have the same 
magnification. The end of the cell opposite the dendrites and hence 
away from the cerebellar crest, is often very slender and pointed. 
This end of the cell body always gives rise to the neurite. These 
cells regularly bear one or more small dendrites which do not enter 
the cerebellar crest and do not possess the small spines (Phot. 45). 
In the case of some cells occupying the same position and having 
the general character of those just described, the dendrites which do 
not enter the cerebellar crest are more numerous and important. 
These cells measure 8—48 by 16—288 w, and are as irregular and 
various in form as can be imagined. The smaller ones which show 
the least resemblance to PuRKINJE cells are comparatively compact 
and regular in form and have numerous small dendrites ramifying 
in the acusticum. The larger cells which approach the PURKINJE 
type are elongated, crooked, and irregular in the extreme. These 
