692 
b. The upper and posterior lobes, connected 
by the single commissure, to be sought for on 
the floor of the posterior notch. 
2. On the inferior surface of the hemi- 
a. The dale, united by the spigot. 
b. The bisentral lobes. ' ; 
c. The slender lobes. 
The biventral lobes and the anterior lamine 
of the slender lobes are united by the pyramid. 
d. The posterior inferior lobes, connected 
by the short and exposed and the long and 
hidden commissures. 
The flocks or lobules of the pneumogastric 
nerve, (lobule of the auditory nerve, Foville,) 
which are situate altogether anterior to the 
hemispheres and attached to each crus, are 
united by the posterior medullary velum, and 
through it appear to have some connection with 
the most anterior portion of the inferior vermi- 
form process. 
A vertical section of either hemisphere of 
the cerebellum or of its median lobe displays 
its structure, and serves further to demonstrate 
the subdivision into lobes above described. 
When either hemisphere is cut in the vertical 
direction, the surface of the section displays a 
beautiful ramification of fibrous matter, the 
smaller branches of which are enveloped by 
lamine of grey matter. This ap nce has 
such a resemblance to the trunk of a tree with 
its boughs and branches, that it early received 
and has continued to retain the name of arbor 
vite. The trunk of the tree is represented by 
a central nucleus of white matter, from the 
upper and lower surfaces of which branch off, 
some at a right, others at an acute angle, 
several lamin, each of which forms the parent 
stem of a number of other branches. Each of 
the primary branches is the foundation or cen- 
tral stem of a lobule. Laminz of fibrous mat- 
ter are seen branching from both sides of it 
immediately after its separation from the nu- 
cleus. Sometimes the primary branch bifur- 
cates, and each division of it forms the stem 
of what may be called a sub-lobule. The ul- 
timate branchings are covered by a layer of 
grey matter. If we suppose that one of the 
primary branches is composed of a certain 
number of lamine of fibrous matter, the se- 
condary ramifications from it will in a great 
degree correspond. In most instances these 
secondary branches subdivide into two or 
more tertiary ones, which, as well as the branch 
from which they spring, are enclosed in grey 
matter. ( Figs. 380, 386.) 
A vertical section of the median lobe gives 
quite a similar appearance to that of the 
hemispheres. The central nucleus breaks up 
into primary branches, which become the centre 
of = lobules of which it consists. ( Figs. 386, 
393. 
The ramifications of the central nucleus, 
whether of the median lobe or of the hemi- 
spheres, separate from it only in the vertical 
eens or from before backwards; in the latter 
irection, however, to a very slight extent. 
Hence these branches are directed only u 
wards, or downwards, or backwards. The 
NERVOUS SYSTEM. (Nervous Centres. Tus Encepnaton.) 
fibrous matter of the median lobe is continuous, 
without any line of demarcation, with that of 
the hemispheric lobules. By reason of this 
disposition of the fibrous matter, the surface 
which is exposed by a horizontal section — 
through the entire cerebellum, presents a very — 
different appearance from that which results 
from a vertical section. It consists of a y 
of fibrous matter bounded on the sides and 
behind by a narrow cortex of grey matter. 
The white matter consists exclusively ¢ 
fibres, chiefly of the tubular kind and of all 
degrees of size. These, in the more distant 
ramifications, penetrate the vesicular matter of 
their grey cortex, and form some unknown cot x 
nection with its elements. The grey matter 
consists of three layers, readily distinguishab' 
by the naked eye from their difference of ec 
a, 
lour. The external layer is the darkest, a 
consists chiefly of granular and vesicular mat- 
ter. The next or intermediate layer is of a 
light colour, and is composed of a stratum of fine” 
nucleus-like particles. The third layer has the 
greatest thickness, and is immediately in con- 
tact with the fibrous matter; it is intermediate 
in point of colour to the other two, and con- 
sists of numerous vesicles of the caudate kind, 
coreeny with branching and nerve- 
tubes of all sizes. The dark colour of the 
external layer is doubtless owing in a grea 
measure to the great numbers of capillary ves 
sels which enter it; the greater paleness of th 
inner stratum is to be attributed to the inter 
mixture of the white fibres, whilst the ligh 
colour of the middle stratum is intrinsic. Fron 
the usual dependent position of the cerebellum 
in the dead body, it always appears to contail 
more blood than the a 
Corpus dentatum.—If, in making a vert: 
oodincnt either hemisphere of the cerebellan 
the incision be made so as to leave two-thit 
of the hemisphere on its outside, a pecu 
will be observed on the surface of the sect 
which deserves a separate consideration. ‘Tl 
central white nucleus is interrupted by a ver 
remarkable undulating line of vesicular matte 
which is convex towards the posterior mat 
of the hemisphere, but open in front 
the crus cerebelli. 
This constitutes the corpus denta 
rhomboideum of the cerebellum. It p 
remarkable resemblance to the structure of 
same name which is met with in the oli 
body of the medulla oblongata. It is evid 
a capsule of vesicular matter which is ene 
in the inner third of the substance of the ¢ 
white nucleus of the cerebellar hemi 
being nearer its superior than its inferio 
face. The peculiar undulating arrangem 
it doubtless has reference to the accom 
tion of a certain extent of surface in a li 
space. The fibrous matter enclosed by it 
derived from the processus cerebelli and 
the restiform body. 7... 
The central stem of fibrous matter to 
the several lobules, both of the hemisphe 
and the median lobe of the cerebellum, adl 
( crus cerebelli, ) is formed by three bund 
fibres, each situate on a different plane- 1 
