ON THE PONS VAKOLII. 517 
strangely maintain, that the development of the cerebellum bears 
a relation to the generative faculty. 
T/fe Decussation of the Brain, —In describing the cerebrum, 
I spoke of the medullary matter of the brain as all tending to¬ 
wards one common centre; and likewise of certain commissures 
or bands, or prolongations of medullary matter, extending from 
one hemisphere to another, and connecting them together. This 
may serve to account for the fact often observed, both in the hu¬ 
man being and the brute, that if a serious injury is inflicted on 
one side of the cerebrum or cerebellum, the effect is referrible to 
the opposite side of the body. Such an effect may also be 
partly accounted for mechanically. 
When a violent blow is received on the cranium, the extrava¬ 
sation of blood, or the injury done to the brain, and sometimes 
the absolute fracture of the bone, is on the other side. The 
pulpy substance of the brain offers to the blow, or to the part of 
the cranium that receives the blow, a yielding resistance that will 
neutralize a very considerable force; but in proportion to the im¬ 
petus which is not thus neutralized, the brain is driven against 
the unyielding bone on the other side, and is injured. Leaving 
this, however, out of the question, I believe it to be a fact, that 
an injury of the cerebrum or cerebellum, or even of the tubercles, 
is often followed by a loss of function on the opposite side of 
the body. It is not so with the medulla oblongata or the spinal 
chord. 
The Pons Varolii. —Now, then, we can once more approach 
the pons varolii. It is the prolongation of the crura cerebelli 
stretching over the crura cerebri; and I beg you to observe, con¬ 
sidering the view which I have just taken of the function of the 
cerebellum, that is at the base of the brain, and corresponds with 
the inferior surface of the medulla oblongata and spinal chord. 
I have already hinted, that the pons varolii is in a directed ratio 
with the corpus callosum, or superior medullary commissure, and 
in an inverse ratio with the corpora quadrigemina and the spinal 
chord. This is the great commissure of the cerebellum, and 
therefore would probably be proportionate to the other, commis¬ 
sures. I have spoken of the corpus callosum in man being large, 
in order to connect together the medullary matter of the fully de¬ 
veloped hemispheres. Compare the bulk of the pons, lessened 
proportionately in the dog, yet more in the horse, and still more 
diminished in the ox. I spoke of the absence of a corpus callo¬ 
sum as the roof of the lateral ventricles in the hare and rabbit, 
as a type of the rodentia. Observe the little pons varolii in 
these animals. 
, The mingling of Medullary Matter under the Pons Varolii .— 
