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I ,
O B S E R V A T I O N S ON THE
C H A P T E R IV.
Of the Communication of the Ventricles of the Encephalori
with each other, by the Author.
S E C T . I.
AF T E R hying open one of the lateral ventricles of the brain in the
ufual w-ay, leaving the feptum between the ventricles entire, let the
gutter which is between the corpora ilriata and thalami nervorum opticorum,
the bottom of which is occupied by the fubftance called Centrum femicirculare
geminum, be traced inwards, and it will be found to lead to
the fore part of an oval hole, large enough to admit a goofe quill, under
the fore part of the fornix. From this hole, a probe can be readily paffed
into the other lateral ventricle, Ihewing, in the firft place, that the* two
lateral ventricles communicate with each other. When the fornix is next
divided tranfvcrfely, we find that this paffage has the anterior crura of the
fornix at its fore part, and the joining or middle part of the choroid plexufes
of the lateral ventricles at its back part, and that its middle part is over
a paffage downwards, named the iter ad infundibulum, or vulva f , which
ihould rather be called iter ad tertium ventriculum.
When we aftenvards carefully raife, and turn backwards the body of the
fornix t , we find that the choroid plexufes of the lateral ventricles are conneSed
together by a broad vafcular membrane, which adheres clofely to
the fornix above it, and to the thalami nervorum opticorum below it.
Hence, too, this membrane covers and fliuts the hole called Anus, and prevents
• Sec Tab. III. Fig. i. and i . F. See alfo Tab. IV. Fig. i. and s. F. F. and Tab. II. S.
t See Tab. III. Fig. 3. F. and Tab. IV. F. 3. F. 4- F.
J See Tab. IV. Fig, 3.
N E R V O U S SYSTEM.
vents the lateral ventricles from communicating with each other, or with
the third ventricle, at any place but that before defcribed. In this membrane
two large veins H H may be obferved, which, farther back, unite to
form a vein known to Galen, and named after him. Two fmall veins on
each fide of the brain, one from the feptum lucidum, the other from the
corpus flriatum, run upon the upper and pofterior edges of the hole by
which the lateral ventricles communicate*, and terminate in the veins
H H.
Under this vafcular membrane, the extent of which, and the degree of
its adhcfion to the fornix and thalami nervorum opticorum, have not been
fuflSeiently attended to, I find the thalami, even in children, infeparably
united by medullary matter. Under the accretion of the thalami, and between
them and the fubjacent crura cerebri, the middle part of the third
ventricle is fituated. From the third ventricle a paffage, univerfally well
known, leads to the fourth ventricle, or calamus fcriptorius f , which is placed
between the tuber annulare, \vith the medulla oblongata on the fore
part, and the cerebellum, with the valvula Vieuffenii and nates and tellea
behind; fo that this ventricle ought to be confidered as a ventricle of the
cerebellum, rather than of the brain.
The bottom of the fourth ventricle has no fueh communication with the
cavity of the fpinal marrow, as Dr HaUer fuppofed, being completely fliut
by its choroid plexus and pia mater J.
In farther proof that the four ventricles communicate with each other,
and that they do not communicate with the cavity of the fpinal marrow, I
have obferved, in the bodies of every one of fifteen children who died from
D internal
• See Tab. III. Fig. i. and 2. Tab. IV. Fig. i. and 2.
t Tiie fubftance called Pineal Gland, which is over this paffage, is evidently a cineritio»! tubercle,
from which medullary matter is fent out.
) See Tab. n. h. and Tab. VI. L.