4 8 B R A I N AND O R G A N S OF THE
I R
(y f I
i-'
Since that time, I have received a work by M. GeofFroi, on the Organ oF
Hearing of Fiilies and other Animals, which was read to the French Academy
in 1753, but was not publiihed till -1778; and find that Dr Camper and
M. Vicq. d'Azir, previous'to the publication of M. GeofFroi, had given an acaccount
of many difcoveries on the fame fubjecl, which they illuflxate by
tables (z).
In the works, however, of thefe authors, the communication of the canals of
the ear with cach other has not 'been fully traced. Little attention has been
paid to the nerves which fupply them; and a very principal part, the external
meatus auditorius, has entirely efcaped their obfervation
I iliall therefore proceed to give a defcription of the ear; firil in the cartilaginous
flat filhes, and then in fome of the oblong-fliaped cartilaginous and in the
ofleous fiflies. After which, I iliall give an account of a few experiments I have
made on hearing in water.
§ 4. Defcription of the Ear of a Skate.
IN the back part of the occiput, near the joining of the head with the fpine,
two holes {a), not larger than to admit the head of a fmall pin, are found at the
diilance of an inch from each other in a large fifh. Each of thefe leads into a
capacious winding canal or concha, which defcribes nearly a complete circle (¿).
T h e two conchae arc feparated from each other by a thin partition (f). Each
concha terminates in a funnel, from which a fmall cylindrical canal or meatus
auditorius externus is continued {et). The meatus is lodged in a hollow left
between two thick cartilages {e); and as there is no membrana tympani, it
opens into a large fac, which contains a white or opake matter, with a quantity
of clear watery-looking, - b u t ^ i ^ ^ , matter ( /). The white fubftance is foft
and cretaccous, eifervefcing violently has a regular fliape; and
yet, in the meatus auditorius externus and concha, generally fome portion of a
iimilar matter is found, as if part of it paiTed off b y the meatus, or was fomehow
neccflary for communicating the imprellion of found to the bottom of the
On
(7) Sec Aaa HarUni, . 1762. « Mem. de Mstli. et de PhyL prts-a I'Ac, R. dci Sclencfj, ti
• M. Geoffioi fays, " L'organc dc I'ouie dc la raye ne paioit point du tout n'eft point
aifce a découvrir. Cachée fous de» mufcles, e!le e(l placée proche les condyles, a leur partie laterale
" la fuivant a l'intérieur, on voit qu'elle donne naiflance a deux canaux} l'un fort court, qui pénétré dans la cavité du
" veftlbule, une fente longue, irreguliere, dont les bords font comme decliirés," &c.
And p. 93. Du trou auditif recouvert des mufcles et de graifle,
Dr Camper, Mcm. de Math. tom. vi. p. 194. denies that tlierc is an externa) opening: " L'organe dc i'ouie dc la raye
" n's donc aucujie communication avec l'air de l'atmofphere} mais il eft enfermé," &c.
And M. Vicq: d'Azir, torn. vii. p. ao. fpeaking of the cartilaginous fittics or nantcs pinnati of Lintwus, fays, "L'orgaiic
de I'ouie iia point, chez eux, d'ouverture exterieurc."
(a) SecTab.VTI.fig.i.fig.z.AA, %. 3. 4.5.
(0 See Tab. VII, {d) Tab. VII. fig. î. rf
( / ) Tab.XXXVn.lig.2 18. and fig, ¡.»b.
(i) Tab. VII. Iig.2. BC. fig. J. 6. 7.
M Tab. XXXVII, fig. 2. ,6. ,
S E N S E S ÏN F I S ' H E S;
On the fore part of the great fac, and communicating with it, a much fmaller
one e is found, which likewife contains both cretaceous and vifcid watery
matter (£). From this fmall fac a du6t e is fent off, which opens into a duft j Ç
common to an anterior and exterior horizontal femicircular canal and the
other two ends of tlicfe femicircular canals join together at i ; and where they
meet, they alfo communicate with the end of their common d u d f . Hence the
large fac b communicates by the medium of the fmall fac d with the anterior
and with the horizontal femicircular canals Thefe again communicate
widi each other, firft by tlieir common duéhJ'-, and in the next place a du<5l:,
formed by their common dud f and by the dud e f rom the fmall fac, joins at
/ with tlic meeting of the other two ends of thefe canals, juft under the end of
the meatus auditorius externus, where it opens into the large fac.
T h e two ends / of the pofterior femicircular canal join- with each other at
n ; and the upper end / communicates diredly with the large fac at k.
When we review the defcription and figures, it appears, that the canals we
have from analogy called femicircular are in the flcate circular ; arid that the caviries
of all of tliem communicate, through the two facs defcribed, with the meatus
auditorius externus.
In each of the femicircular canals there is a dilatation or pouch, iliaped like
that part of our red veins at which valves are found ; yet there are no valves in
them.
T h e anterior and ""pofterior circular canals confift of an upper and under por-»
rion ; between which there is a thin ligament pp which ferves as a fupport to
them.
T h e large fac refembles our veftible ; and the fmall fac has fome likenefs to
the tube wliich in birds feems to fupply the place of the cochlea.
T h e membrane of the drum and the cavity of the tympanum are wanting ;
which, as the found is not conveyed by the air, wc ijiigiic ii priori have fappofed
would be the cafe : and the meatus auditorius externus performs the office
of the Euftachian tube -, at lead fo far as that tube may be fuppofed to fei-ve the
purpofe of diicharging uieleis or hurtful matter. The circular canals are fille4
with a vifcid liquor fimilar to that in the large fac. The membrane which
compofes them is tranfparent, but thick and pretty tough ; and even when diftcnded,
they are fo much fmaller than the canals of cartilage which contain
them, that between them and tlic cartilage there is a vifcid watery liquor contained
in a cellular fubftance ; on the threads of which, veiTels both circulating
and abforbent, and nerves, are difperfed (¿).
Thefe facs and circular canals are furniihed with very large nerves, derived
from nerves which rcfcmble our fifth and feventh pairs (/).
T h e anterior and horizontal circular canals are fupplied from the fifth pair;
the facs and poilerior circular canal arc fupplied frofn the fifth and feventh
N pairs
(f) In Tab, XXXVII. fig. 3. tliefe faea and the fcmicireular canal» ate very accuralcly delineated j to which therefore this defer!
pi ion chic ft y refers,
(J}) See XXXVII. fig, 4. i t r f . ' / (¿) Tab. XXXVII. fig. t. and 4. 27—34. and35. ¡é. 37.
I I I S L -