i l
64 O B S E R V A T I O N S ON THE
eye than the ciliary circle, or, that it covercd that part only of the bottom
of the eye on which the pictures of objeds can be diftindly painted.
T o demonftrate more clearly the extent of the retina, in feme of my
iirit cOLirfes of anatomy, I ufed to pour a few drops of reftified fpirit of
wine on it, which inftantly renders it much more opake than natural, and
thereby makes its termination much more diftindly vifible ; but I obferved,
that, in a ihort time thereafter, a fomewhat fimilar opacity is communicated
to fuch part of the lens as the fpirit touches, and, to an inattentive
obferver, fuggefts the idea, that the retina is continued to cover
it ; or, if we do not diileft the eye till fome time after it has been immerfed
in ardent fpirits, the capfule of the lens and retina appear fo nearly of
the fame colour, that we are apt to fuppofe the one to be the continuation
of the other.
I am therefore perfuaded that Dr Haller has been milled, (particularly
in the difleftion of the eyes, reprefented in his Fafeiculus Anat. VII.
Tab. VI. fig. 7. & 8. which feem to have been injeded and preferved in
fpirits), by not having fufficiently attended to the eiïeds which ardent fpirits
have of coagulating the lens, and giving it an opacity like to that of
the retina.
5. In 1753, when I received Dr Meckel's elaborate treatife on the 5th
pair, I obferved, that, by an unaccountable error, the trunk of the internal
carotid artery is reprefented by him as pafling between the fécond and
third branches of that nerve ; whereas it is on the inner fide of both ; and
hence that his new-difcovered reileded branches of the fifth pair are reprefented
quite out of their real place. I demonftrated this error by a preparation
I made at that time ; a figure of which the reader will find in
Tab. XXVI I . *.
6. Although,
• See Tab. XXVII.
N E R V O U S S Y S T E M . 6 j
6, Although, from the great fenfibility of the teeth, it is evident they
are provided with nerves; yet one of the latefl writers on that fubjed has
alledged, that thefe cannot be profecuted by difiedion *. But I have,
twenty years ago, obferved, and demonftrated, firft. That the proper inferior
maxillary nerve is fenfibly fmaller where it goes out of the hole at
the chin, than where it enters the canal at the inner fide of the jaw-bone:
In-the next place. That the nerves of theteeth can not only be diftindly
traced from their trunks, but that, in a child at birth, their feveral branches
can be plainly ihown, firft conneded fo as to form a plexus, and after that
entering the pulp of the tooth. Other branches pafs between the teeth to
the gums f .
7. Several celebrated authors J have affirmed, that, if the recurrent nerves
are cut, the voice is entirely loft. But as the larynx receives a pair of fuperior
laryngeal, as well as recurrent nerves, my father, long ago, ventured
to exprefs a fufpicion, that fuch experiments had not been made with
fufScient accuracy ||. In 1752, I found proof that this was reaUy the
cafe ; for, at that time, affifted by the ingenious Dr Emmett, now State
Phyfician in Dublin, I cut thofe neves in a fmall dog, and obferved, that,
although the voice of the animal was very fenfibly altered in tone, and
weakened, yet it was far from being loft; nay, in the courfe of fix weeks,
the ftrength of the voice was in a confiderable degree reftored. Hence
there was reafon to conclude, that each of the mufcles received branches
from the fuperior laryngeal nerves. Since that time I have found, on diffeding
the nerves of the human larynx, that the recurrent and fuperior
laryngeal nerves are joined together by their apices, or that they form a
R plexus,
• Mr J. Hunter, on Teeth, p. 42. fays, ' By injeflions we can trace the blood-velTels diftinaiy through
' the whole cavity of the tooth; but I could never trace the nerves diftinaiy even to the beginning of
' the cavity.'
t See Tab. XXV.
1 Galen, Vefalius, Bidloo, La Motte, Riolan, Chirac, Valfalva, Morgagni, Martin.
It See his Treatife on the Nerves, 1741.