NERVOUS CENTRES. (Human Anatomy. Tuer Encrpnaton.) 
inserting the handle of a knife along the pos- 
terior margin of the cerebellum, this fissure 
may be shewn to pass forwards to a consider- 
able depth, and to communicate on each side 
with the semilunar fissure, whilst it is inter- 
rupted in the middle posteriorly, by the notch. 
Its inner surface is lined by a process of pia 
mater, which sinks into it. 
The right and left cerebellar hemispheres 
exhibit a general symmetry, which is, however, 
not always perfect, as a manifest ditference is 
sometimes observable in their sizes. And a 
corresponding want of symmetry may be fre- 
_ quently seen in the right and left fosse of the 
occipital bone. 
_ Both the hemispheres and the median lobe 
_ are composed of an assemblage of laminz 
_ closely applied to each other. Each lamina 
_ consists of a thin layer of white or fibrous 
matter, between two of grey or vesicular sub- 
_ Stance, which are continuous along the outer 
Besargin of the former. Thus the exterior of the 
_ cerebellum consists of a stratum of vesicular 
Matter, which forms a cortex to the enclosed 
white or fibrous substance. The lamin are 
_ separated from each other by fissures, and they 
__ are covered by pia mater, which adheres closely 
_ to them, and penetrates to the floors of the fis- 
sures. 
The laminz are collected into sets on the 
_ Superior as well as on the inferior surface. Each 
set forms a lobe. Each lobe is surrounded by 
_adeep fissure, which separates it from the next 
_ adjacent lobes. 
It is necessary to distinguish the fissures 
_ which separate the lamin from those by which 
_ the lobes are bounded. The former are very 
Shallow: the latter are deep, and penetrate 
quite to the central stem of the hemisphere. 
By removing the pia mater carefully from 
the surface of the hemispheres, and from the 
deep fissures, the shape and boundaries of the 
lobes may be clearly demonstrated. Or if a 
_ vertical section of a hemisphere be made, the 
deep fissures may be readily distinguished from 
the superficial ones which separate the laminz ; 
and in this way also the lobes may be demon- 
‘strated 
i 
& 
_ The floor of each deep fissure is formed by 
white matter. And as the deep fissures inter- 
vene hetween the lobes, lamine of the lobes 
constitute their walls, and the superficial fis- 
sures which separate these lamine open into 
m. 
On the superior surface of the cerebellum 
two principal lobes may be distinguished. 
ese are the square lobe and the posterior 
ior lobe, according to the nomenclature 
of Reil, whose descriptions cannot be sur- 
eS) in minuteness or accuracy. ( Fig. 390, 
> . 
The anterior margin of the square lobe over- 
hangs the semilunar fissure ; its posterior mar- 
gin isa little behind the level of the floor of the 
cd notch. By careful separation of its 
mine or by a vertical section, it may be 
Shewn to consist of eight lobules, each having 
a stem of fibrous matter derived from the cen- 
tral one of the hemisphere. 
VOL, III. 
689 
The posterior superior lobe (P, fig. 390,) 
forms the posterior part of the superior surface 
of the cerebellum ; its posterior margin is that 
of the hemisphere ; the horizontal fissure sepa- 
rates it from the posterior inferior lobe. It is 
separated from its fellow of the opposite side by 
the posterior notch. 
On the inferior surface of each hemisphere 
the following lobes are readily distinguishable. 
( Fig. 391.) We enumerate them, passing 
from before backwards. 
1. The amugdala, so called from its resem- 
blance to an enlarged tonsil. This and its 
fellow of the opposite side form the lateral 
boundaries of the anterior extremity of the 
valley, and are in great part covered by the 
medulla oblongata. 
2. Behind the amygdala is the biventral 
lobe, wedge-shaped, narrow towards the valley, 
wide towards the semilunar fissure. Its lamine 
are curved with their concavity forwards and 
inwards, and it is united with its fellow of the 
opposite side by lamine which cross the val- 
ley forming part of the inferior vermiform 
rocess. 
3. The slender lobe, which consists of a few 
lamine curved parallel to the posterior ones of 
the biventral lobe. 
4. The inferior and posterior lobe, which 
extends to the posterior edge of the hemi- 
sphere. The inner margin of each of these 
lobes constitutes the lateral boundaries of the 
posterior notch. 
Such is the constant disposition of the supe- 
rior and inferior surfaces of the cerebellum. 
A defect of symmetry is sometimes apparent 
in the inequality of corresponding lobes; but 
those above enumerated are always present. 
So definite an arrangement must obviously have 
some physiological import. What that may 
be it is impossible even to conjecture, and 
we must be, for the present, content with a 
concise statement of the facts of the anatomy. 
Some analogy exists between this arrangement 
and that of the convolutions on the surface of 
the brain, many of which exhibit a constancy 
of position and form quite as remarkable. 
The median portion of the cerebellum is also 
composed of lamine, which are continuous with 
those of the hemispheres, but their arrangement 
on the superior and inferior surfaces is so diffe- 
rent as to demand a separate description. On 
the superior surface the lamine are separated 
from each other by fissures, in the same way as 
those which constitute the hemispheres, and 
they are collected into sets forming lobes which 
correspond to and connect those of the lateral 
hemispheres. These lamine are curved, their 
anterior margin being very slightly convex 
(fig. 390). The edges of these laminz, as they 
le in close apposition, resemble the segments or 
rings of a worm; whence the term vermiform 
las been applied to this as well as the inferior 
surface of the median lobe. The lamine take 
for the most part a vertical direction, with the 
exception of the anterior and posterior ones, 
which pass gradually to the horizontal, the free 
margins of the former being directed forwards 
and those of the latter backwards. The pos- 
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