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NERVOUS CENTRES. (Human Anatomy. Tut Encepuatoy.) 
eessus cerebelli ad testes, all connect neigh- 
bouring parts with the intrinsic matter of the 
mesocephale. 
It is plain, then, that anatomy affords abun- 
dant grounds for the conclusion, that the me- 
socephale must be regarded as a distinct centre, 
connected by numerous bonds of union with 
the other segments of the brain. 
If further proof of this were wanting, it 
would be found in the connexion of two im- 
portant nerves with this segment. These are 
the fifth and the fourth pair. The former pene- 
trate between the superficial fibres of the pons 
which spread out upon the crus cerebelli; the 
latter are connected with the superior surface 
of the mesocephale. 
Or THE CEREBELLUM.— (rageyxeParss, 
omscbsos eynearss; Fr. cervelet ; Germ. Kleine 
Gehirn.) This remarkable portion of the ence- 
phalon, so called from its general resemblance 
to the cerebrum, of which it is, as it were, the 
diminutive, is situate behind the mesocephale 
and medulla oblongata. It is lodged in a com- 
rtment of the cranium, the floor of which is 
ormed by the fossz of the occipital bone, and 
which is separated from the cavity occupied by 
the cerebrum, by the horizontal process of the 
dura mater, previously described as the tento- 
rium cerebelli. This process forms a partition 
between the inferior surface of the posterior lobes 
_and the superior surface of the cerebellum. 
The cerebellum, like the cerebrum, is at its 
highest point of developement in the human 
subject. 
__ the encephalon in all the classes of vertebrate 
_ animals, and exlibits a marked gradation of 
increase from Fishes, through Reptiles and 
_ Birds, up to Mammals. 
It exists as a very distinct portion of 
In Fishes and Reptiles it consists of a sin- 
gle lobe, overhanging the posterior surface of 
é medulla oblongata, and closing the fourth 
ventricle partially like a valve. It is, in ge- 
neral in these classes, smooth on its surface, 
and exhibits no complication of structure, no 
Subdivision into lamine. But in the sharks 
@ manifest increase in size and an incipient 
lamellar arrangement are distinctly observable, 
which shew that in them this organ is more 
highly developed than in any other fishes. 
In birds a similar complication of structure 
takes place to a much greater extent, and a 
lateral lobe or appendage is added on each side 
to the single central organ which constitutes 
the cerebellum of fishes and reptiles. And in 
the mammiferous series, the lateral lobes along 
with the central portion experience a progres- 
Sive augmentation of size (proportionally to the 
dy), and a corresponding complexity of 
Structure up to the quadrumana and man. 
The best and most obvious subdivision of 
the human cerebellum is into the median lobe 
and the lateral lobes or hemispheres. The 
former is the fundamental and primitive portion 
of the organ; the latter, although each exceeds 
the median lobe in size, and therefore they con- 
Jointly form far the largest portion of the 
cerebellum, are appendages, which in man 
assume great physiological importance. The 
median lobe has likewise been called vermi- 
687 
form process, the upper and lower lamine 
being distinguished as the superior and inferior 
vermiform processes. 
From the tables already given it would ap- 
pear that the cerebrum is to the cerebellum in 
the proportion of 8 or 9 to 1 in the adult, and 
in the infant, according to Chaussier, as 16 or 
18 to 1. The average weight of the cere- 
bellum is, according to Professor Reid’s re- 
searches, 50z. 4dr. in the male, and 4 oz. 
12 dr. in the female. 
The cerebellum seems to keep pace, in its 
developement, with that of the cerebrum. It 
attains its greatest size, both in male and fe- 
male, at the same age as the cerebrum. 
At the most advanced ages, however, it seems 
to diminish with greater rapidity than that 
organ. 
Some variety appears to occur as regards the 
relative developement of cerebellum to cere- 
brum in the adult. Chaussier remarks that he 
had in some instances found the cerebellum 
equal to a seventh or a sixth part of the weight 
of the cerebrum, but rarely the eleventh or 
twelfth. 
There do not appear to be any good grounds 
for the assertion that the cerebellum is more 
developed in proportion to the brain in the 
female than in the male. Professor Reid’s 
extensive series of researches show, beyond all 
question, that it maintains the same propor- 
tionate bulk in both sexes. 
It has also been asserted that castration, or 
disease of the genital organs, such as would 
destroy the generative instinct, causes wasting 
of the cerebellum. If both testicles be re- 
moved, the whole cerebellum, it is said, dege- 
nerates; if only one, the hemisphere of the 
opposite side is affected. 
The most complete refutation of this assertion 
is afforded by M. Leuret’s series of observations 
of the brains of geldings and entire horses. 
These researches, indeed, shew that in stallions 
the cerebellum is proportionally smaller than in 
mares or geldings, and that in geldings it is 
larger than in mares. It is very evident from 
them that mutilation of the sexual organs does 
not cause degeneration of the cerebellum. 
The shape of the cerebellum is that of “ an 
ellipsoid flattened from above downwards.”* 
Its principal diameter, which is transverse, is 
from three-and-a-half to four inches in length ; 
the antero-posterior diameter is from two in- 
ches to two inches and a half; the anterior part 
is about two inches in thickness; whilst near 
its posterior edge it does not measure above 
half an inch. 
Atitsanterior edge the cerebellum is notched, 
and receives fibres by which it is connected to 
the cerebrum and mesocephale. This notch is 
of considerable transverse extent, and is semi- 
lunar in shape. The greater portion of the 
posterior part of the mesocephale corresponds 
to it. By Reil this is called the semilunar fis- 
sure. In it we find several parts which the 
anatomist should study; namely, on the highest 
plane, the processus cerebelli ad testes, sepa- 
* Cruveilhier. 
