ANATOMY. 
quantity, as to induce a slight degree of 
deafness, which is easily removed by syring- 
ing with warm water. 
The membrana tympani, which is a circu- 
lar membrane above a quarter of an inch in 
diameter, is stretched across the inner 
extremity of the meatus, and derives its 
name from a comparison with a drum head, 
to which it bears some analogy in its use. 
In the fetus it is stretched on a distinct 
bony ring, called the annulus auditorius. 
This ring is deficient at its upper part, and 
has no bony union to the rest of the tempo- 
ral bone, but it becomes united soon after 
birth. 
This membrane is concave on its exterior 
surface, and convex towards the tympanum. 
Its position is inclined, the upper margin 
being more towards the outside of the bead, 
and the under part farther inwards ; so that 
the superior part of the meatus forms an 
obtuse angle, and the inferior part an acute 
angle with the membrane. 
The internal ear consists of two divisions, 
viz. the tympanum and the labyrinth. 
The tympanum is an irregular bony ca- 
vity, which will about admit the end of a 
finger, hollowed out of the temporal bone, 
just within the membrana tympani. It has 
several communications with the neighbour- 
ing parts. 
Opposite to the membrana tympani are 
two openings, which lead to the labyrinth 
of the ear. The upper one is named the 
fenestra ovaiis, the lower one the fenestra 
rotunda, and the projection between them 
is called tne promontory. The fenestra 
ovaiis is filled, as we shall presently see, by 
one of the little bones of the tympanum, 
and the fenestra rotunda is closed by a 
membrane. 
The eustachian tube, or iter a palato ad 
aurem, opens in front of the tympanum. It 
commences by an expanded cartilaginous 
orifice at tne back of the nostrils, passes 
through the substance of the temporal bone, 
and terminates by a contracted orifice in 
the tympanum. Its office is to convey air in to 
the cavity of the tympanum. The membrana 
tympani is thrown into vibrations by the im- 
pulse of the sonorous undulations of the air 
and that vibration could not take place un- 
less there was air in the inside as well as on 
the outside ot the membrane. Water, or 
any other fluid, would not have answered 
the purpose. Hence an obstruction of this 
tuba causes deafness, which surgeons have 
attempted to remedy by puncturing the 
membrana tympani. An opening in the 
latter membrane of a small extent does by 
no means injure hearing ; for many persons 
have the power of impelling tobacco smoke, 
or agitating the flame of a candle through 
the ear, and yet seem to have a perfect use 
of the organ. In these cases the air or 
smoke enters the eustacliian tube from the 
throat, and passes through the unnatural 
aperture in the membrane. 
The mastoid process of the temporal bone 
is composed internally of numerous cells, 
communicating with each other, and finally 
opening into the back part of the tympa- 
num. These do not exist in the fetus. 
The cavity of the tympanum contains a 
chain of small bones, called ossicnla auditus, 
connected by one end to the membrana 
tympani, and by the other to the fenestra 
ovaiis. Ot these the first, which is com- 
pared to a hammer, is called the malleus ; 
the second is named the incus, and the fluid 
the stapes. 
The malleus possesses a manubrium, or 
handle, a long and short process, and a head 
which forms an articular surface. 
The incus resembles a grinding tooth, 
with its two fangs diverging. We remark 
in it a body, the surface of which is hollowed 
out to receive the head of the malleus ; a 
long and a short leg. 
The stapes has an exact resemblance to 
the iron part of a stirrup ; it has a head, two 
crura, and a basis. 
The handle of the malleus is firmly con- 
nected to the membrana tympani; and 
hence arises the external concavity and in- 
ternal convexity of the membrane. The 
head of that bone is joined to the body of 
the incus, whose long leg is articulated to 
the head of the stapes. The basis of the 
stapes fills up the fenestra ovaiis. The ends 
of the bones forming these articulations are 
covered with cartilage, and furnished with 
capsules like other joints. 
The bones of the tympanum have some 
small muscles connected to them, by which 
they are moved outwards, or towards the 
membrana tympani, and inwards, or towards 
the fenestra ovaiis. The first of these mo- 
tions relaxes, the latter stretches the mem- 
brane. The names of these muscles are, 
tensor tympani, Iaxator tympani, and sta- 
pedeus. 
The nerve called chorda tympani passes 
across the tympanum, between the handle 
of the malleus and the long leg of the incus. 
The use of the ossicula auditus seems to 
be that of transmitting the vibrations of the 
air from the membrana tympani to the 
