“only 
PHYSIOLOGY OF THE NERVOUS SYSTEM, 
traction of the pupils. Longet found that re- 
moval of one optic thalamus in the rabbit was 
followed by paralysis on the opposite side of 
the body. It appears, however, that this was 
done after the removal of the hemisphere and 
corpus striatum, whereby the experiment was 
so complicated as to invalidate any conclusion 
that might be drawn from it respecting the 
function of the thalamus. Indeed, vivisections 
upon so complex an organ as the brain are ill- 
calculated to lead to useful or satisfactory 
results; but one does not hesitate to refer to 
such as have been made, because they afford a 
certain amount of negative information, imper- 
fect though it be. 
Nothing definitive respecting the proper 
office of the thalami can be obtained from pa- 
thological anatomy. Extensive disease of 
these bodies is attended with the same phe- 
nomena during life, as lesion of similar kind 
in the corpora striata. Hemiplegic paralysis 
accompanies both; nor does it appear that sen- 
‘sation is more impaired when the thalamus is 
diseased, than when the corpus striatum is 
affected. 
There is nothing in the phenomena attendant 
on morbid states of the thalami which can be 
fairly regarded as opposed to the conclusion 
which their anatomical relations indicate, name- 
ly, that they form a principal part of the centre 
of sensation. The intimate connection between 
the striated bodies and the thalami sufficiently 
explains the paralysis of motion which follows 
disease of the latter; whilst, as the thalami do 
Not constitute the whole centre of sensation, but 
a part thereof, it cannot be expected that 
lesion of this part would destroy sensation, so 
Jong'as the remainder of the centre on the same 
side, as well as that of the opposite side, retain 
their integrity. Complete paralysis of sensation 
‘on one side is very rare in diseased brain: a 
- slight impairment of it frequently exists in the 
early periods of cerebral lesion, apparently as 
an effect of shock; for it quickly subsides, 
although the motor power may never return, 
According to the views above expressed, the 
‘corpora striata and optic thalami bear to each 
other a relation analogous to that of the ante- 
rior to the posterior horn of the spinal grey 
ter. The corpora striata and anterior horns 
} are centres of motion; the optic thalami and 
posterior horns, centres of sensation. The 
‘anterior pyramids connect the former; the 
| olivary columns, and perhaps some fibres of 
the anterior pyramids, the latter. The olivary 
columns, however, are in great part continu- 
| ations of the thalami on the one hand, and of 
the grey matter of the cord on the other; and 
‘contain abundance of vesicular matter, in which 
herves are implanted. 
And it must be admitted that the intimate 
connection of sensation and motion, whereby 
Sensation becomes a frequent excitor of mo- 
tion,—and vol motion is always, in a 
state of health, attended with sensation,— 
would @ priori lead us to look for the respec- 
tive centres of these two great faculties, not 
only in juxta-position, but in union at least as 
intimate as that which exists between the corpus 
722N 
striatum and optic thalamus, or between the 
anterior and the posterior horns of the spinal 
grey matter. 
Saucerotte, Foville, Pinel Grandchamps, and 
others, advanced the opinion that the corpora 
striata and the fibrous substance of the anterior 
lobes of the brain had a special influence upon 
the motions of the lower extremities, and that 
the optic thalami and the fibrous substance of 
the middle and posterior part of the brain pre- 
sided oyer the movements of the upper ex- 
tremities. We find, however, but little to 
favour this theory either in the results of ex- 
periments, in pathological observation, or the 
anatomy of the parts. Longet states, that, in 
his experiments upon the optic thalami, the 
paralysis affected equally the anterior and the 
posterior extremities. | Andral analysed se 
venty-five cases of cerebral lesion limited to 
the corpus striatum or optic thalamus. In 
twenty-three of these cases, the paralysis was 
confined to the upper extremity: of these, 
eleven were affected with lesion of the corpus 
Striatum or of the anterior lobe; ¢en with lesion 
of the posterior lobe, or of the optic thalamus; 
and two with lesion of the middle lobe.* 
Hence it is plain that a diseased state of the 
corpus striatum is as apt to induce paralysis 
of the upper extremity as lesion of the tha- 
lamus ; and we are forced to conclude, that 
pathological anatomy is not competent to de- 
cide the question. Lastly, the anatomy of these 
two bodies renders it highly improbable that 
they perform a function -so similar, as that of 
directing the movements of particular limbs, 
The great size of the optic thalamus, its mul- 
titude of fibrous radiations, its extensive con- 
nections both in the medulla oblongata and in 
the hemispheres by means of commissural 
fibres, the marked difference of its structure 
from that of the corpus striatum, its con- 
nection more with the posterior horns of the 
spinal grey matter than with the anterior ones, 
and its intimate relation to nerves of sensation, 
are sufficient anatomical facts to warrant the 
opinion that the thalami must perform a func- 
tion which, although it may be subservient to, 
or associated with, that of the striated bodies, 
is yet entirely dissimilar in kind. 
It has been supposed that the corpora striata 
are special centres or ganglia to the olfactory 
nerves, and to the sense of smell. But such 
a supposition is altogether superfluous, imas- 
much as a very distinct and obvious centre to 
these nerves exists in the olfactory process or 
lobe, miscalled nerve by descriptive anatomists. 
The small olfactory nerves are implanted in 
the anterior extremity or bulb of this process, 
which is provided with all the structural cha- 
racters of a nervous centre, and contains a 
ventricle. This lobe, moreover, is always de- 
veloped in the direct ratio of the size and 
number of the olfactory nerves, and of the 
developement of the sense of smell; and in 
the Cetacea, a class in which the olfactory 
nerves and process either do not exist at all, 
or ate so imperfectly developed as to have 
* Clin. Med. t. v. 
2 7 2 RRERER 
