O B S E R V A T I O N S ON TH£
C H A P T E R 1 1 .
Of the Membranes of the Brain and Cerebellum in general.
A FTER removing the cianium and the dura mater, the latter of
which, befide the offices already mentioned, ferves as periofteum to
the inner layer of the cranium, and as a cufliion to defend the brain from
the bone, we find the brain and cerebellum covered by two membranes called
the arachnoid coat and pia mater.
The arachnoid coat has no veflels which convey red blood, and is extremely
thin and tender. At the bottom of the brain it is eafily demonftrated;
but at the top of the brain it is much lefs evident.
The pia mater covers not only the external furface of the brain and cerebellum,
and enters by proceiTes or doublings into all their furrows, but alfo
lines certain cavities called the Ventricles.
I would obferve, however, that there are not only fewer large veflels
difperfed within the ventricles than upon the furface of the brain, but that
there are fewer fmall veiTels, as we cannot, by an injedion, make the pia
mater, lining them, fo red as that on the furface of the brain.
C H A P .
N E R V O U S SYSTEM.
C H A P T E R III.
Of the Communication of the Ventricles of the Encephalon
with each other, as defcribed by other Authors.
^ fl ^ H E R E are four ventricles within the human encephalon, to witj
two called lateral ventricles within the hemifpheres, into which the
brain is divided : A third ventricle lies under a feptum, between the lateral
ventricles : A fourth is fituated between the tuber annulare and cerebellum.
Thefe cavities have been defcribed by Galen, and by many fucceeding
Authors of eminence, as all communicating with each other*; and the
fourth ventricle has by fome eminent authors, particularly by Dr Haller,
been fuppofed to communicate with the cavity of tlie fpinal marrow •{•.
The manner of the communication of the third ventricle with the fourth
has been generally well underftood.
A hole or paflage at the upper and fore part of the third ventricle has
not only been defcribed, but painted by different authors, under the name
of Vulva J . A few authors likewife have mentioned a place under the for-
C nix,
• Galen de Ufu parcium, Lib. 8. cap. Vefalius de C. H. Fabrica, Lib. 4. cap. Spige-
U u s d e H . C . Fabrka, Lib. 10. cap. 8. Aramius, Tab. Anatom. Lib. 10. Bauhinus, Th. Anat.
Lib. 3. cap. 13 VieuiTens, Neur . Univ. Lib. i. cap. Willis, Cerebri Anatome, Cap. 2. p. 10.
Ridley, Anat. of the Brain, Cap. 13 Cowper, Ap. to B. Verheyen An. Lib. 4. cap. 6.
Winflow, An. Tr. de la Tefte, 70. 81. 84. ^Heifter, C. Anat. 270. p. 135.
t Haller, EI. Phyf. Ub. 10. S. 2. § 6. p. 77. et S. 3. § 7. p. 87.
i Vefalius An. L. 7. T. 6. et 7 Arantius, Lib. 10. T. 4- 5- 6 Vieuffens Neur. Tab. 7. 8.