1002 
Fishes is moved by six muscles analogous to 
those met with in other Vertebrata, and to 
which similar names are applicable. The recti 
muscles (fig. 532, 1, 2, 3,4) are four in 
number, arising from the back of the orbit 
near the margin of the optic groove, and run- 
ning forward to be attached in the usual manner 
to the sclerotic coat of the eye. The obliqui 
(fig. 532, a, 6) both take their origin from the 
anterior part of the walls of the orbit, and pass 
ina transverse direction towards the eyeball, into 
which they are inserted, one on its superior, the 
other on its inferior aspect. There is no troch- 
lear apparatus in connection with the superior 
oblique, as is the case in quadrupeds, but, like 
the inferior, it passes straight to its destination. 
The suspensory or choanoid muscle met with 
in Mammalia, in Fishes is totally wanting. 
In the Sharks the muscles moving the eye- 
ball are of very great strength, and, moreover, 
their efficiency is rendered more perfect by me- 
chanical contrivances that are not met with in 
the ordinary Fishes. In the latter the eye is 
simply supported in the orbit by a quantity of 
loose cellulosity filled with a gelatinous or fatty 
semifluid substance, admirably adapted to faci- 
litate the movements of the eye; but in the 
plagiostome cartilaginous Fishes the cartilagi- 
nous pedicle is provided, already mentioned, 
which, taking its origin from the back of the 
orbit between the origins of the recti muscles, 
runs forward to be moveably articulated, fre- 
quently by means of a very complete ball- 
and-socket joint enclosed in a capsular liga- 
ment, to the back of the selerotic, so as to 
form a pivot upon which the eye turns. In 
the attachment of the recti and oblique mus- 
cles to the eye-ball an additional piece of me- 
chanism is observable, each of these muscles 
being inserted into a prominent cartilaginous 
tubercle, which projects from the external sur- 
face of the sclerotic, and thus enables the 
muscle to act with greater advantage. 
In the generality of Fishes there are no eye- 
lids, the external tegument passing on to the 
front of the eye-ball without forming any fold 
or duplicature to which such a title is appli- 
cable; there are, however, exceptions to this 
arrangement which must not be passed over 
unnoticed. Thus, in the Mackarel (Scomber 
Scombrus ), the eye is partially defended by two 
vertical folds of the common integument, and 
in the Herring ( Clupea Harengus ) there is a 
similar provision for the defence of the eye-ball 
and orbit.* The vertical folds are unprovided 
with any muscular structure for their move- 
ment, and are consequently transparent so as 
not to interfere with vision when the front of 
the eye is brought beneath them. It is worthy 
of observation that, where these folds decussate 
one another at their inferior extremities, the an- 
terior one overlaps the posterior, so slight an 
impediment to progressive motion as the con- 
trary position would have occasioned having 
thus been foreseen and avoided. 
In the Sharks and Sturgeons the integument 
* Vide Catalogue, Mus, Coll. Surgeons, Lond. 
vol. iii. p. 171. 
PISCES. 
forms a deep circular fold around the front of 
the eye, which, although motionless, is evidently 
of a palpebral character. A secreting membrana 
conjunctiva is reflected deeply between this cir- 
cular fold and the globe of the eye, of which it 
covers the anterior half. In the Sharks* there 
is likewise a third eyelid, which is moveable; 
this is placed at the inferior and internal or 
nasal side of the orbit, and is moved over the 
front of the eye in a direction upwards and out- — 
wards by means of a strong round muscle (nic- 
titator ) which arises from the upper and poste- 
rior or temporal side of the orbit, and descends 
obliquely to be inserted into the lower and 
outer margin of the third eye-lid; passing in 
this course first through a muscular trochlea, 
and then through a_ligamento-cartilaginous 
loop. The trochlear muscle is not, however, — 
exclusively subservient to the action of the — 
nictitator, but has an insertion in the upper — 
part of the palpebral fold, which it depresses — 
simultaneously with the raising of the third — 
eyelid, a slight external groove above the upper — 
eyelid indicating the extent of motion all 
The lacrymal apparatus is totally wanting in 
the whole race of Fises, no trace of lacrymal 
glands or puncte lacrymalie being ever distin= 
guishable; neither could a lacrymal secretion” 
be needed in animals whose eyes are 
ally bathed by the water in which they live. 
Auditory apparatus.—The organ of hearing 
in Fishes undergoes a gradual improvement in 
its structure as we advance from the lower to t 
more highly organized genera, presenting alme 
every intermediate gradation the le 
complex form, in which it consists of the 
bule alone, without semicircular canals or other 
appendages, approximating in simplicity the 
ear of a Cuttle-fish (vide art. pgp ; 
to the most complete icthyic the 
auditory apparatus, a with in the Sharks 1 
Sturgeons. * 
It is in the Lampreys (Petromyzon) that 
the auditory organ exists in its humblest state ~ 
of developement.t In these Fishes the ear is 
enclosed in a simple cartilaginous capsule 0 
an elliptical figure, situated on each side of the 
skull external to the posterior cranial cartilages. 
The walls of these capsules are thin, and th 
cavity which they contain of an ovoid sha’ 
In that side of each cartilaginous capsule 
(vestibulum cartilagineum, Weber,) which is 
nearest the cranium, are two openings, th 
inferior, which is the larger, being of an a 
shape closed with a firm and elastic membrane, 
while the superior is extremely small, givin 
transit to the auditory nerve as it passes into 
the vestibule. With the exception of these 
apertures, which open into the cavity of the 
cranium, the cartilaginous capsule is closed on 
all sides. 
The whole of the elliptical cavity of 
cartilaginous capsule is filled by a pellucid 
membranous sac (vestibulum membranaceum ) 
€ 
“ 4 
x Catalogue, Mus. Coll. Surgeons, Lond. p a 
+ Vide Tract. de Aure animalium aquatilium, — 
= Ernesto Henrico Webero. Lipsia, 1820. — 
to. : 
