zoo 
860 
the comparatively small eye of the opossum (didelphis mar- 
supialis); the whale has the smallest. No mammalia have 
it so slightly convex on the surface as man. 
The following numbers give the proportions of the three 
humours, measured on the axis of the eye, after it had been 
frozen. 
Aqueous Humour. Crystalline. Vitreous Humour. 
Man. 4 . 3 4 j. M 
Dog...&••••.A. 
Cow.. ..••••M. 4? 
Sheep..$.-W. 
Horse ..$ 5 ....j|..H 
Owl..... &...... M- .••••* 
Herring....4.-f. t 
A lacrymal gland exists in all animals of this class. 
The nictitating membrane, (membrana nictitans, palpebra 
tertia, seu interna, periophthalmium) of which only a rudi¬ 
ment exists in the quadrumana and the human subject, is 
very large and moveable in some quadrupeds. This is the 
case in animals of the genus felis, in the opossum, the seal, 
and particularly in the elephant. 
Of the organ of hearing.—In the class vermes the sepiae 
only have any thing like an organ of hearing. In the car¬ 
tilaginous ring, to which the large tentacuia of the animal 
are affixed, two oval cavities appear, in each of which is a 
small bag, containing a bony substance, and receiving the 
termination of nerves. 
There is no doubt that several insects possess the sense of 
hearing; but the organ of this sense is very uncertain. In 
some of the larger animals of the genus cancer, a part can be 
distinguished, which seems to be analogous to the vestibu- 
lum of the former classes. A small bony tube is found on 
each side at the root of the palpi: its external opening is 
closed by a firm membrane; and it contains a membranous 
lining, on which a nerve, arising from a common branch 
with that of the antennse, is expanded. 
Fishes possess near the anterior cervical vertebra consi¬ 
derable ossicula, which may be compared to the malleus, in¬ 
cus, and stapes; and in those which are provided with a 
swimming bladder, these bones are so connected with that 
organ as to render it probable that it is auxiliary to the sense 
of hearing. 
Their internal ear consists of three large canals, which are 
generally seen to project into the cavity of the cranium. Op¬ 
posite to the termination of the auditory nerves on the vesti- 
bulum, one, two, or three neatly formed stones are found. 
These are as white as porcelain, particularly in several of the 
bony fishes, and very dry and brittle in their texture. 
The internal ear of fishes is distinguished from that of the 
other three classes of red-blooded animals, by this remarkable 
peculiarity, that it grows as the fish increases in size, and 
consequently that its magnitude is in the direct ratio of the 
bulk and age of the animal. 
Turtles, frogs, and most species of the lizard kind, possess, 
besides semicircular canals, a tympanum and Eustachian 
tube, like warm-blooded animals. Both the latter parts, 
however, as well as the ossicula auditus, are wanting in the 
salamander. The foramen ovale in this animal is merely 
closed by a portion of cartilage, and the vestibuium contains 
a soft stone. 
The serpents, with a very few exceptions, as the blind- 
worm, (anguis fragilis) have neither tympanum nor Eusta¬ 
chian tube. They have a kind of rudiment of ossiculum. 
The want of a cartilaginous external ear is compensated in 
birds, particularly in those of the rapacious kind, by the 
regular arrangement of the feathers round the opening of the 
meatus. Several also, chiefly of the last mentioned class, 
and particularly among the owls, have a peculiar valve 
placed at the opening, partly of a membranous, partly of a 
muscular structure. 
They have a single ossiculum auditus, connecting the 
membrana tympani with the fenestra oval is, and conse¬ 
quently supplying the place of the malleus and stapes of the 
mammalia. 
ZOO 
The Eustachian tubes have a kind of common opening 00 
the arch of the palate. 
The labyrinth is distinguished by large canals,, projecting 
from the cranium, and not hollowed out of a hard bony sub¬ 
stance, as in most mammalia, and by the want of cochlea. 
The four-footed mammalia are the only animals which 
possess true external ears; and, even in that class, several in¬ 
stances occur in which these parts are wanting. 
The external auditory passage is furnished with a valve in 
such animals as go frequently into the water, by which they 
can close it when they dive: the water-shrew (sorex fo- 
diens) affords an example of this structure. 
All mammalia have a membrana tympani, a tympanum 
situated within this, and an Eustachian tube passing from 
that cavity to the fauces; except in the cetacea, where it 
opens in the blowing hole. The membrane is rather con¬ 
cave on its outer surface, being slightly depressed in the 
middle. All the animals of this class are furnished with the 
two fenestra; the fenestra ovalis, which is filled by the base 
of the stapes; the fenestra rotunda, at which the scala tym¬ 
pani of the cochlea commences. 
In the horse and ass the Eustachian tube does not open 
immediately into the larynx; but into a sac peculiar to this 
class of animals, which is situated on the lateral parts of the 
lower jaw. 
In most of the four-footed mammalia, there is connected 
with the tympanum another cavity; which, according to the 
situation of the bony organ that contains it, must be com¬ 
pared to the mastoid cells in the temporal bone of man. 
In several animals this organ forms a mere bony cavity, 
(bulla ossea) viz., in the dog, cat, martin, squirrel, hare, and 
some of the bisulca. 
Warm-blooded quadrupeds have, like the human subject, 
three ossicula auditus; which on the whole resemble in form 
those of man. But the ducked-billed animal, whose structure 
in every respect is so anomalous, has only two. 
Cuvier has found that the stapes is nearly solid in the ceta¬ 
cea ; and that there is no perforation in the walrus. This 
peculiarity of structure seems to belong to such mammalia as 
live in water; for the seal has it in a smaller degree.— Lemon's 
d'Anat. comp., tom. ii. p. 505. 
The labyrinth of the ear seems to agree on the whole, in 
its essential points, with that of the human subject. But the 
cochlea has in some cases a turn more than in man. 
The ossicula auditus and the labyrinth are remarkably 
small in the cetacea. 
ZOOM, a small river of the Netherlands, in North Bra¬ 
bant, which falls into the East Scheldt, at Bergen-op-Zoom. 
ZOOPHO'RIC COLUMN, s. A statuary column, or a 
column which bears or supports the figure of an animal. 
Johnson. 
ZOO'PHORUS, s. [£«op<jj>os, Gr.] A part between the 
architraves and cornice, so called on account of the orna¬ 
ments carved on it, among which were the figures of ani¬ 
mals. Johnson. 
ZO'OPHYTE, s. [^aoipvTov, of and tpviov, Gr.; zoo¬ 
phyte , Fr.] Certain vegetables or substances which partake 
of the nature both of vegetables and animals.—They appear 
in grammar, like Zoophytes in nature, a kind of middle 
beings, of amphibious character. Harris. 
In the Linnaean system, the zoophytes, which constitute 
the fifth order of worms, (see Vermes,) are composite ani¬ 
mals, resembling a flower, and springing from a vegetating 
stem. This order contains 14 genera, as the Tubipora, 
Madrepora, Millepora, Isis, Antipathes, Gorgo- 
nia, Alcyonium, Spongia, F lustra, Tubularia, Co- 
raixina, Sertularia, Pennatula, and Hydra : see 
each respectively. The species enumerated and described in 
Gmelin’s Linnaean system are 489. 
ZOO'TOMIST, s. A dissector of the bodies of brute 
beasts. Johnson .—It should rather be defined a dissector of 
animals, since his occupation is not confined to the dissection 
of beasts, but birds, fishes, insects, &c. 
ZOO'TOMY, s. [^coroyia, of ijaov and tc/avco, Gr.] Dis¬ 
section of the bodies of beasts. 
ZOPFINGEN, 
