551 
terior part of the skull. By this latter method, especially, a view 
may be obtained of the cerebellum and cerebrum as they lie in situ. 
Owing to the transparency of the dura mater in many of the lower 
mammals, the relations of these structures to each other may be 
studied, either with or without the removal of this membrane. 
Comparative anatomists, in describing these relations, are in the 
habit of employing such terms as overlapping, covering, exposure, 
denudation, to express their extent. Such terms are not, however, 
sufficiently precise, because they do not convey distinctly which sur- 
face of the cerebellum it is which is thus overlapped, covered, ex- 
posed, or denuded. Indeed, it is seldom that the attempt has been 
made, in the lower mammals, to give an accurate definition of these 
surfaces, so as to distinguish them from each other. Before a close 
and accurate comparison can be instituted between the relations of 
the cerebrum to the cerebellum in man and other mammals, it is 
necessary that such a definition be attempted. It has appeared to 
me that the septum lying between the cerebrum and cerebellum, 
commonly termed the tentorium cerebelli, furnishes us with a basis 
for arriving at a precise conclusion. 
If we turn to the descriptions of the cerebellum of man, given in 
our standard text-books of human descriptive anatomy, we shall find 
it stated that the cerebellum consists of a central median part — the 
vermiform process, or worm ; and of two lateral lobes — the hemi- 
spheres. Of these, the hemispheres preponderate greatly in size. 
The cerebellum presents an upper and lower surface, and a circum- 
ference. The upper surface corresponds to the tentorium cerebelli ; 
the lower is lodged in the concavity of the inferior occipital fossse, 
to which it is accurately adapted. The circumference of the cere- 
bellum corresponds to the line of junction of the upper and lower 
surfaces with each other, and along it a deep fissure, the great 
horizontal fissure, extends. The circumference — called also the 
posterior margin — corresponds, therefore, to the line of attachment 
of the tentorium to the transverse line of the occipital bone, and 
marks with great precision the divergence of the two surfaces of the 
cerebellum from each other. Of these surfaces, that which is supe- 
rior, and in contact with the tentorium, which we may therefore 
appropriately term tentorial, is the only one related to the cere- 
brum, the posterior lobes of which not only cover, but even project be- 
yond it. The inferior surface, in contact with the occipital bone, 
