7ro 
are met with in the brain. The peculiar struc- 
ture of particular parts, as the opie thalami, 
corpora striata, tuber cinereum, &c. has been 
already described. , 
The grey matter of the convolutions of the 
brain presents the same characters throughout, 
excepting in certain convolutions of the poste- 
rior lobe near the posterior and inferior horns 
of the lateral ventricles. Here, we may ob- 
serve, in a horizontal section, the grey matter 
of the convolutions separated into two portions 
by a delicate white line, well represented in 
Jig. 398. This layer of light matter was first 
Fig. 398. 
White line in the grey matter of convolutions of the 
posterior lobe. 
described by Vicq d’Azyr, but has attracted 
very little attention from subsequent anatomists. 
I have never looked for it without finding it. 
It consists of nucleated particles, similar to 
those in the grey matter of the cerebellum. 
The layer of grey matter external to it contains 
few nerve-fibres ; that internal to it contains them 
in great numbers, passing into it at right 
angles. 
It is not intended in this part of the article 
to discuss the physiology of the brain. But in 
order to develope more clearly than can be 
done in a mere description the connection of 
its several parts and the views of its struc- 
ture which i believe to have the best founda- 
tion, I shall state briefly what appears to be the 
probable modus operandi of the organ, whether 
as the source of voluntary action or as the re- 
cipient of sensitive impressions. 
It will be necessary first to state the follow- 
ing earn as postulates. 
1. The vesicular matter is the source of ner- 
vous power. In mental actions it is the part 
immediately associated with changes of the 
mind : whether in the working of the intellect, 
or in the exercise of the will, or in the per- 
ception of sensitive impressions. 
2, The convolutions are the parts immedi- 
ately concerned in the intellectual operation. 
3. The simple exercise of the will, for a 
voluntary movement, is probably connected 
with the corpora striata. 
4. The mere reception of sensitive impres- 
sions is connected with the optic thalami and 
the superior layer of the crus cerebri. 
NERVOUS SYSTEM. (Nervous Centres. Tus Encepnaton.) 
- cord; from their small size it is highly imy 
5. Mental emotions affect the posterior and 
superior part of the m ‘ baal 
6. The cerebellum is the regulator of the 
locomotive actions. ae 
These propositions, which, it is admitter 
although not improbable, are far from be’ 
proved, will serve as the basis of an hypot 
of the action of the brain. a 
In apf operations of thought, as in th 
exercise of the reasoning powers, or of thos se 
the imagination, the convolutions of the br 
are immediately engaged. We do not say’ 
material changes give rise to the mental action 
but rather that the changes of the immate 
mind and those of the vesicular matter o! 
conyolutions are simultaneous. 
If an intellectual act gives rise to the 
cise of the will, the change in the super 
vesicular matter is propagated by the fibr 
the hemisphere to the corpus striatum, where 
the will is excited, and the change in the ve 
cular matter of that body is od alon 
the inferior layer ee the crus i, and 
passing through the mesocephale, along the: 
terior pyramids to the spinal cord, each an 
rior pyramid acting u that antero-late 
column of the cord which is on the opr 
side of the body to itself. 7 
The pyramids connect the vesicular mai 
of the corpora striata with that of the 
oe 
Wr 
4 
. 
bable that they can be viewed as continuat 
of spinal nerves up into the brain. 
Simple solution of continuity of the» 
of the hemispheres, which does not ca 
pressure, nor affect in any way the cor 
striata, would therefore merely cut off 
communication between the seat of intelle 
action and the centre of voluntary action. 
will, although unaffected, is unable to 
up with the train of thought, and mental | 
fusion is the result. The loss of speec! 
sometimes precedes a paralytic attack, 
which may remain even after the paralysis 
been wi ti may be accounted for in 
way. e intellect is competent to 
the thought, but unable to excite the 
upon which the exercise of the organs of s 
is so obviously dependent. % 
Changes, originating or excited in 
hemisphere, may be propagated to the 
sponding parts of the other hemisphere 
transverse commissures, the 
anterior commissure, &c. How far 
mispheres are in simultaneous action 
the rapid changes of the mind in thoug 
scarcely be determined; it seems pr 
however, that, in certain acts of volition 
only is the seat of the change which prot 
the movement. If I will to move m 
arm, the change by which that moyem 
prompted belongs to the left hemisphe 
corpus striatum. rua 
ertain cases of disease confined to: 
misphere, in which a considerable de 
least, of intellectual power persists, : 
that the sound one may suffice for the m 
tation of the changes connected with th 
and it may be reasonably su thi 
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