THE EAR AND HEARING. 
199 
THE EAR AND HEARING. 
BY W. J. ABEL, B.A., F.R.M.S. 
(Continued from 169,) 
The walls of the tympanic cavity are bony, lined with 
mucous membrane, and ciliated. The inner wall contains two 
orifices leading into the internal ear, and closed by a membrane 
somewhat similar to the tympanic. The larger of these open¬ 
ings (the fenestra oralis) is oval, the smaller (the fenestra 
rotunda) is round. We may, perhaps, explain the use of these 
openings by noting that in passing from air to water directly, 
sonorous vibrations are greatly weakened, but that the interpo¬ 
sition of a tense membrane between the two media greatly 
intensifies the vibrations. Crossing the tympanum is a chain 
of very small bones—the Malleus is attached by its slender 
end, or handle, to the tympanic membrane,—the Incus —a 
bicuspid tooth-shaped bone, rests by its body on the head of 
the malleus, whilst the longer of its two fang-like processes is 
articulated by a round tubercle, by some called the orbicular 
bone , with the Stapes which covers with its base the fenestra 
ovalis. These beautiful little bones have synovial membranes 
and capsular ligaments at their articulations, as in the case of 
the other perfect joints of the body, and are covered by 
mucous membrane reflected from the tympanic walls. Any 
vibration which, passing up the outer canal, affects the tym¬ 
panic membrane, is conveyed with great intensity through 
these bones to the fenestra ovalis, the membrane of which is 
thus strongly agitated. The movements of the tympanic 
membrane cause the long processes of the malleus and incus 
to swing like a pendulum upon the axis furnished by the short 
processes of these two bones. 
Two distinct theories are offered as to the route 
which the sonorous vibrations follow—1. That they pass 
through the ossicles merely, causing both molar and 
molecular vibration ; and 2, That the air in the drum is set 
vibrating by the outer membrane. The considerations guiding 
our preference are (a) the drum is not a perfectly closed cham¬ 
ber, and any vibrations excited in its contained air would be 
liable to escape by the eustacliian tube; (b) its internal sur¬ 
face is constantly moist, but moisture tends to deaden vibra¬ 
tion ; (c) the bones form a complete link across the drum, 
and it is well known that solids conduct vibrations more 
rapidly and forcibly than fluids ; (d) they are covered with a 
