NERVOUS CENTRES. (Iluman Anatomy. Tus Encrpnaton.) 
sound hemisphere may excite to action the 
centre of volition (corpus striatum) on the dis- 
eased side. ; 
The existence of hemiplegic paralysis, then, 
implies an affection, direct or indirect, of the 
‘centre of volition (corpus striatum) on the op- 
posite side. Pressure, or a morbid change in 
the physical state of its tissue originating in it 
or propagated to it, is all that is necessary for 
this purpose; and this change, like the change 
in the normal actions, may be of such a kind 
as to elude our means of observation. 
When a sensation is excited, the stimulus 
acts from periphery to centre. The change is 
propagated by the sentient nerve to the optic 
thalamus, which, by its numberless radiations 
and its many commissures, is well calculated 
to excite all parts of either hemisphere, and 
| even of both hemispheres. When the nerve 
ened is one of pure sense, the change is 
_ wrought more directly in the brain; if the fifth, 
_ orany of the nerves of the medulla oblongata, 
the stimulus acts directly on the part; but if a 
nerve of either limb be stimulated, the change 
_ must be propagated through the spinal cord. 
It will be asked, if this be the modus ope- 
randi in sensations, how does it happen that 
disease of one optic thalamus does not impair 
Sensation in one-half of the body? And how 
is it that such disease is much more frequently 
_ associated with hemiplegic paralysis, of a kind 
“not to be distinguished from that which de- 
pends on diseased corpus striatum. The answer 
to the first question is as follows. The optic 
thalamus, or, more properly, the centre of sen- 
_ Sations, is never wholly diseased, for this centre 
is not confined to the optic thalamus of descrip- 
_ tive anatomists, but extends to the mesocephale 
and olivary columns. Extensive disease of 
_ this centre would probably be fatal to sensa- 
tion. But the most ample provision exists for 
‘Opening up new channels of sensation if those 
on one side or a part of them be impeded. 
The centres of opposite sides are intimately 
5 , especially in the medulla oblongata 
‘and mesocephale, by commissural or by decus- 
‘ating fibres; the optic thalami of opposite 
sides are connected to each other by the poste- 
Tior commissure and the soft commissure, and 
the immense multitude of fibres which radiate 
from each thalamus insure its connection with 
a considerable extent of the brain, so that a 
change in any part of it cannot fail to be com- 
‘Municated to some portion of the hemisphere. 
It is sufficient for mere sensation that the centre 
of sensibility should be affected. Intellectual 
change resulting from that affection depends 
upon fibres which radiate between it and the 
optic thalami. 
_ Itofien happens that at the onset of a cerebral 
} lesion sensation as well as motion is paralysed 
| in the opposite side of the body. Ina few days, 
| however, the sensibility returns whilst the pa- 
| ralysis of motion remains,—a fact which is 
| sufficient to show that the motor and sensitive 
power must have different channels in: the 
| centres as well as in the nerves. The primary 
paralysis of sensation may be due to a lesion 
on one side affecting the centre of sensibility, 
711 
or to the shock which that centre may have 
received from the sudden occurrence of lesion 
in some other neighbouring part. In the latter 
instance the recovery of sensibility takes place 
evidently on the subsidence of the effects of 
shock : in the former it may depend on the 
existence of other channels of sensitive impres- 
sions, independently of those involved in the 
lesion. Hence there may be lesion of one 
optic thalamus without loss of sensibility. 
The answer to the second question is ob- 
tained from considering the intimate connection 
of the corpus striatum and optic thalamus. 
No two parts of the brain are so closely united 
by fibres in vast numbers passing from one to 
the other. Disease of the thalamus therefore 
may excite a morbid state of the corpus 
striatum, without producing any change in its 
structure, which may be recognised by the or- 
dinary means of observation. And thus he- 
miplegia will take place, and remain as long 
as the morbid state of the corpus striatum re- 
mains. A lesion of the corpus striatum may 
in a similar manner affect the optic thalamus 
of the same side; but as that is not the only 
channel of sensitive impressions, a loss of sen- 
sibility does not necessarily occur. 
Emotions are for the most part excited 
through the senses. A tale of woe, a dis- 
gusting or painful spectacle, a feat of won- 
derful power or skill, the sudden appearance 
of a person not expected, are calculated to 
produce corresponding emotions of pity, dis- 
gust or pain, wonder or surprise. But emo- 
tions may likewise be produced by intellectual 
change. The workings of the conscience 
may remind one of some duty neglected or 
some fault committed, and the emotion of 
pain, or pity, or remorse may ensue. Now 
emotion may give rise to movements indepen- 
dently of the will. The extraordinary influ- 
ence of emotion on the countenance is well 
known, and this may affect one -side of the 
face, which is paralysed to the influence of the 
will, or it may excite movements of the limbs, 
even when the will can exert no controul over 
them. From these facts it is plain that that 
part of the brain which is influenced by emo- 
tion must be so connected that the convolu- 
tions may affect it or be affected by it; that it 
may be readily acted on by the nerves of pure 
sense; that it may influence the spinal cord 
and the motor nerves of the face when the 
ordinary channels of voluntary action have been 
stopped. No part possesses these conditions 
so completely as the superior and posterior part 
of the mesocephale, which we have already 
noticed as concerned in acts of sensation. Is 
an emotion excited by an impression made 
upon one of the senses? this part becomes 
directly affected, and through the optic thala- 
mus the emotional feeling causes intellectual 
change. The working of the intellect on the 
other hand may act on the seat of emotion 
through the same channel. And an excite- 
ment of this part may produce movement of a 
limb, or of all the limbs, through its influence 
on the spinal cord through the olivary columns. 
The cerebellum influences the antero-lateral 
