44 B R A I N AND ORGANS
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The fabcUvifions of the brain and cerebellum, or their tuberclcs and lobes,
are more numerous than in the mammalia or birds; and in die various genera
of fiilies, the differences of thefe are fuch, as to iliow the vanity of attempting to
determine the office of each lobe or tubercle of the brain.
Ganglia are wanting in their nerves.
In one genus of fiihes, the gadus, I have found fpheroidal bodies between the
dura and pia mater, and covering the greater part of their nerves, like a coat of
mail, in their courfe towards the organs to which they are deftined. That this"
obfervation may be intelligble to the reader, I have fubjoined Tables reprefenting
them («), which I formerly publiihcd in my work on the Nervous
Syftem.
After thefe few general obfervations on the brain, we ffiall proceed to confider
the organs of the fenfes, and particularly the nofe, the ear, and the eye ; for on
thofe of touch and tafte I find little or no room for remark.
S E C T . II.
O/" the Organ of Smell in FiJfjes.
J N all fiilies, external openings or noftrils for fmell are very evident, generally
two on each fide in the offeous fiihes (iz), which, on each fide of the head
lead to a complex organ, the furface of which is of conliderablc extent; and
upon them a pair of large or olfactory nerves terminates, with the addition of
fome branches from nerves rcfembling our fifth pair (c). In fome fiilies, as in
the haddock, I have obferved thar cte-olfadtory nerve, in its courfe between the
head and the nofe, pafTes tlirough a cineritious ball {d), refembling the cineritious
matter conneded in our body to the olfaflory nerve within the cranium.
There can therefore be no doubt that they enjoy the fenfe of fmelling : nay,
there is great reafon to believe, that, fuited to their furrounding element, they
are much more fenfible of odorous bodies diflblved in water, and applied by its
medium, than we ihould be, if the application of the objedl was to be made to
our organ of fmell by the fame medium.
(i) SteTib.n. II. Tab. XL. fig. i. and z.
(ii) S«e Tab.XXXI. fig. i. K.
(i) Tab. XXXI. fig. I.
{c) Tab.XXXI. 00.
S E C T .
S E N S E S IN FISHES.
S E C T . III.
Of the EAR in Fijhes.
Of the Ear la the Cetaceous FiJ}:es.
J T is well known that the ear of the whale-kind refembles that of man; and
feveral authors, particularly Dr Tyfon and Dr Camper (e), have publiflied
an account of the feveral parts which compofc it; but I have not been able to
procure either of thcfc works. I obferve, from the Commentarii Liplienfes (/),
tliat Dr Camper denies that they have femicircular canals; a circumftance in
which I apprehend this eminent author to be miftaken. He is alfo uncertain
whether they have an Euftachian tube. I ihall for thefe reafons, as well as for
the fake of conneilion, give a fliort account of what I have obferved in the diffedlion
of the phocsna, one of the cetaceous order.
On each fide of the head there is a round hole {g), fcarcely large enough to
admit the head of a fmall pin, which is the beginning of a long meatus auditorius
externus (Jo); at tlie bottom of which we find a concave membrana tympani
(f). The membrana tympani is conneded to the bottom of the cavity of
the tympanum by a chain of fmall bones, tied together by a reddiih-coloured
membrane. The innermoit piece, analogous to our ilapes, has evidently a
mufcle connected to it ; a large nerve or portio mollis divides into two
branches, and then enters the bone at the bonom uf the cavity of the tympanum
or OS petrofum (/): and foIJowing one of the branches of the nerve, we
are led to the cochlea, which is divided by a feptum into two fcala; each of
which contains a reddifli-coloured tube, that is cafily feparable from the oiTeous
canal which contains it (;«).
Following the other branch of the nerve, I obferved part of the femicircular
canals the membrane of which is very thin {«), and adheres to the bone which
contains it.
The cavity of the tympanum is remarkably large, and communicates freely
with otlier cavities which are analogous to our frontal, fphenoidal and maxillary
finufcs (o).
A tube, fimilar to our Euftachian tube, or iter a palato ad aurem, begins to-
M wards
(<•) Tyfoii on ihc Pliocain. Camper afla Harlem.
(/) Com. Lipficns, vol. xvii. p. 460.
(0 S« Tab. XXXV. fig. 5- I. fig. 6. I.
(/) See T.ib. XXXV. fig. 7. T S.
<•;) Sec Tab. XXXV, fig. 8. X.
xvii. in 1765 and 1776.
See Tab. XXXV. fig. i. F. {h) Tab. XXXV. fjj. j. F G.'
(.<) T.-.b.XXXV. fig. 6. KLM.
(«) Tsb. XXXV. fig, 8. U W, aod fig. 9. W YZ.
{0) Tib. XXXV. fig, 6, NOPQ_R,