700 
however, do not form any intricate interlace- 
ment as in ganglia, but are collected into bun- 
dies of very variable size; the largest being 
placed at the inferior part of the body, the 
smallest towards the hemispheres. The free 
or ventricular portion of the corpus striatum 
contains comparatively few fibres. When a 
portion of the striated part of the body is 
examined under the microscope, the nerve- 
fibres, of which the bundles are composed, ap- 
pear to be reduced to their smallest size, and 
to be very compactly applied to each other, 
so that they transmit very little light, and 
therefore put on the appearance of dark cylin- 
ders. It is only by very high powers that we 
can discover their fibrous structure. In many 
of the bundles the fibres appear to terminate 
at one extremity as if by forming an adhesion 
around a large vesicle, faint indications of the 
nucleus and nucleolus of which may be some- 
times seen through the surrounding fibres. The 
appearance which the fibrous cylinders which 
exhibit this structure present calls to mind 
very strongly the representation of the nucleus 
of a comet with its tail. And this peculiarity 
of structure may be adduced as an argument 
that many if not the greater number of the 
fibres of the striated body form intimate connec- 
tions with the elements of its vesicular matter. 
Optic thalami.—In the internal concave sur- 
face of each corpus striatum, the optic thala- 
mus is placed. The latter body is therefore 
sewed and internal to the former. The 
ighter colour of the optic thalamus distin- 
guishes it at once from the corpus striatum. 
The optic thalami come into close relation to 
each other by their inner surfaces, which form 
the lateral boundaries of the third ventricle. 
Each optic thalamus, like the corpus stria- 
tum, presents a free and an attached portion. 
The Poeiton projects into the ventricle—the 
intra-ventricular portion ; the latter adheres to 
the inner side of the corpus striatum and to 
the mass of the hemisphere, and posteriorly, to 
the olivary columns, the quadrigeminal tuber- 
cles, and the processus cerebelli. The supe- 
rior surface is free and forms part of the floor 
of the lateral ventricle; the internal surface is 
likewise free-and forms the lateral wall of the 
third ventricle, being, however, interrupted in 
a very small space by the adhesicn of the soft 
commissure. A portion of its external and 
posterior surface is also free, and projects back- 
wards and outwards into the inferior horn of 
the lateral ventricle, presenting a pointed ex- 
tremity in that situation. These free surfaces 
are smooth and moist, being covered by the 
membrane of the ventricles. The velum in- 
terpositum, which again is overlapped by the 
fornix, rests upon i superior surface of the 
optic thalamus. 
The optic thalami are placed obliquely, so 
that they are nearer each other at their anterior 
than at their posterior extremities. Each mea- 
sures about an inch and a half in length, nine 
to ten lines in height, and about eight lines in 
breadth. In colour they are very much lighter 
than the striated bodies, and they appear to be 
NERVOUS SYSTEM. (Nervous Centres. Tae Encepnaton.) 
covered with a delicate layer of fibrous matter. — 
A band of fibrous matter passes along the inner 
surface of each from behind 
posteriorly is connected to the pineal gla 
and forms, with its fellow, the peduncles of 
that body. = 
Beneath the posterior free extremity of the 
thalamus, situated in the angle between that 
body and the superior surface of the crus, wi 
find a small rounded eminence of a dark; 
grey colour Paes n= by very numerous fora- 
mina for the transmission of bloodvesse 
This is the corpus geniculatum internum, 
Lower down and more external and anterior, 
there is another similar body, somewhat smalle 
and less dark, the corpus geni ernum. 
Both of these bodies are connected with the 
quadrigeminal tubercles. A band of fibrous 
matter passes from the testes to the external 
geniculate body, and from the nates to the in- 
ternal one. si 
In point of structure the thalamus resemble: 
a ganglion much more closely than does the 
corpus striatum. A light reddish is the 
colour of the surface when cut into ; it be 
not inappropriately compared to that of coffe 
mixed with . good deal of milk (café au lait) 
When thin sections are examined, are founc 
to consist of very numerous fibres interlacin 
freely, with nerve vesicles occupying their in- 
tervals. The fibres are not coll into bun 
dles as in the corpus striatum, nor do they take 
a radiating course in the thalamus, The reti 
wiped oath form is very like that i 
e ganglia on the posterior spinal roots. 
The fibres of the optic thalami, i I 
they are very numerous, have extensive. con 
nections. Along its ventricular surface the 
are evidently continuous with those of the he 
misphere, which appears to radiate from it 
the grey matter of the convolutions. Posterior 
the fibres of the processus cerebelli ad te 
and those of the olivary columns pass into 
The anterior pillars of the fornix are connecte 
with it in front, and derive from it some nervoi 
fibres ; and below and within, a cylinder | 
fibres emerge from it to the mamillary bodie 
Thus the optic thalami are connected with 
hemispheres on one hand, with the olivary ¢ 
lumns and with the cerebellum on the ¢ 
hand. The quadrigeminal tubercles pla 
upon the processus cerebelli may have so 
connection with them through the bun 
of fibres. Although these bodies have b 
viewed as having a special connection with 
optic nerves, it does not appear that | 
nerves have any relation to them but thi 
the geniculate bodies or the quadrigem 
tubercles. It is important to bear in m 
respecting the optic thalami that they are 
rectly continuous with the superior portio 
the crus cerebri, so that in viewing a ver 
section of the encephalon we see no Ii 
demarcation between. The thalamus gi 
as it were, from the superior extremity of th 
crus; it is recognised from the latter by 7 
swelling into an ovoidal mass. It is ¢ 
tically, as Willis long ago expressed it, 
‘ 
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