It:
ir:
It A
(•
l'i
l„ ìk
B R A I N AND O R G A N S OF THE
pairs conjoined. After reacliing the facs and canals, and running a little way
upon their membranes, they lofe their white colour, become pellucid, and difappear.
§ 5. ^ Defcripuon of the Ear of the Squalus Squatina of Limans.
IN thf fqualus fqaadna, or angel fiih, another of the fiat cartilaginous fiihes,
I have found the ftruflure of the organ of hearing to agree fo nearly with that
of the ikate, that I think it unneceiTary to obferve farther, than that the external
meatus auditorii are found at nearly the fame place, to wit, over the upper
and pofterior part of the head near its joining with the fpine (/•). Within the
external orifice there is a winding concha K, from which a fmall cylindrical
meatus L leads into a large fac or veftible M, filled with a vifcid watery humour
and cretaceoiis foft fubi tance; and with this tliree circular canals N O P
communicate.
^ 6. A Defcriptim of the Ear in fom of the long-fbaped Cartilaginous Fifia^ and in the
Offeous Fifhes.
AT the lower end and poilerior 'part of the fides of the cranium, feparated
f r om the brain by membranes only, we find the organ of hearing fituated in the
ofieous fiilies, and in fome at leaft of the oblong-iliaped cartilaginous fifties. I
have cliiefiy examined the cod and the ilurgeon. In both, the organ confifts of
three femicircular canals, to wit, an anterior and pofterior perpendicular canal,
and a middle horizontal one (/).
Each-of the-perpencíiculzii-«uaals.iias^a dilated portion or bulb at one of its
ends, where it joins with the horizontal cánal and in the anterior of thefe in
the cod, a fmall fcabrous calcareous ftone is lodged (ji). The anterior end of
the horizontal canal is likewife dilated (0).
T h e fmall upper ends of the anterior and poilerior femicircular canals join
together, and form a common canal, which defcends perpendicularly {p).
The horizontal femicircular canal has its large end joined to the bot tom of the
anterior canal, and its fmall end joins with the under end of the poilerior femicircular
canal
Thefe common canals open into the under part of the perpendicular cana!,
and
(/) See Tab. XXXVllI, F G H H I. (/J Tab. XXXIX. K L M N O P. and Tab, XL, fig. 3. and 4. A B C D E F G.
(w) S« Tal). XXXIX. fig. ..and 4. LP. and Tab. XL. fig. 3. and 4, B D. («) Tab. XXXIX. fig-3.
W S« Tab. XXXIX. fig, I.and 4. LL. and Tab. XL. fig, 3.and4.EE.
(/) See Tab. XXXIX. fig, i, and 4, K. and Tab. XL. lig,4, G.
(7) Sec T.-ib. XXXIX. fig. I. and 4, and Tab. XL. fig. 4'
S E N S E S F I S H E S, &C.
and of courfe meet there, and communicate freely with that canal and with
each other (r).
W e next find a fac of confiderable fize, in which a large fcabrous calcareous
ftone is lodged (j). This large ilone, as well as the fmaller in the femicircular
canal,, feems to be furrounded b y a vifcid humour.
A hole or opening in the fore or under part of the common, perpendicular
canal leads into this'fac in the ilurgeon ( f ) : but I have not obferved any fuch
opening in the cod or haddock.
Very large nerves are fixed to the bulbous parts of the femicircular canals;
and fpreading out on thefe canals, they become fuddenly peUucid («).
On the fac which contains the large ilone, efpecially of the cod, a confiderable
nerve is fpread in a moft elegant manner (x).
The femicircular canals and large fac contain, befides the ilones, a vifcid
humour; and as the femicircular canals are much fmaller than the'canals of
bone or cartilage which contain them, fo we find a quantity alfo. of vifcid humour
between their outer part and the bones or cartilages.
In the cod, haddock, and perhaps the whole genus of gadus, a number of.
fmall fpheroidal bodies, which I have obferved to form part of their nervous
fyilem, is to be found in this vifcid humour fupported by fmall fibres of veiTels
and of nerves (y).
I have alfo in the cod obferved a bag about the fize of a pea a little farther
back than the pofterior femicircular canal, filled with vifcid humour, and witli
a nervous filament from the nerve which fupplies the large fac; and which I
fuppofe to be part of the ear (z).
I have not, however, been able as yet to difcover in thefe fiihes any meatus
auditorius externus.
(r) See Tab. XXXIX. fig. i. and 4. K. and Tab. XL. fig. 4,
r.) See Tab. XXXIX. fig. i. and 2. Tab. XL. fig. 4. H I.
f-0 See Tab. XXXIX. fig. ¡.and 4. Q.RS.
OJ See Tab. XXXIX, fig, 1, and 4. T.
(/) Tab. XL. fig. 4. I.
(r) Tab. XXXIX. fig. i. and 4. R R:
(:) Tab. XXXIX, fig. 4. V.
C H A P .