200 
THE EAR AND HEARING. 
moist membrane which, by being a bad conductor of vibra¬ 
tions, tends to prevent the vibrations passing through them 
being weakened by diffusion, and (e) in the internal ear there 
are six separate canals, with five of which the fenestra ovalis 
communicates, and, being covered by the stapes, air vibrations 
would be obstructed in their passage to the labyrinth through 
it, whilst the fenestra rotunda, which is exposed, communicates 
only with one of the internal canals. Hence the vibrations 
would seem to be transmitted through the bones, partly by 
their molecular, but chiefly by their absolute movement. The 
theory of mixed transmission through the co-operation of air 
and bones seems untenable, inasmuch as vibrations travel 
through them with different velocities. Edouard Weber 
thought the fenestra rotunda, by means of its elastic covering, 
acts as an adjunct to the fenestra ovalis, facilitating the 
approximation and removal of the stapes from the labyrinth, 
by its alternate compensating movements towards and from 
the tympanic cavity. 
The Labyrinth (the essential part of the organ of hearing) 
consists of a small bony chamber, called the vestibule, three 
semicircular canals (two vertical and one horizontal), and a 
structure called, from its resemblance to a small shell, the 
cochlea, all hollowed out of the hardest (petrous) part of the 
temporal bone. 
The Vestibule is a small irregular chamber about the size 
of a grain of barley. Leading from it are the five openings of 
the three semicircular canals (three in the posterior and 
lower, and two in the superior horn)—several openings in 
its inner wall for the entrance of the auditory nerve filaments, 
—the fenestra ovalis in its outer wall,—the opening leading to 
the cochlea in its inferior and anterior wall—and in its posterior 
wall an opening called the aqueductus vestibuli, with uncertain 
contents and office. The vestibule contains two distinct 
membranous bags—the larger, oval in shape, called the common 
utricle , from which spring the three membranous canals lining 
the bony semicircular canals; the smaller bag somewhat 
globular (hence called the sacculus hemisphericus ).—It com¬ 
municates with the middle chamber of the cochlea (the 
Scala Media). The membranous labyrinth contains a watery 
fluid called endolymph, whilst it is separated from the bony 
labyrinth by a similar fluid called the perilymph. These 
fluids contain small particles, composed of carbonate and 
phosphate of lime, to which their discoverer, Brescliet, gave 
the name of otoconia (ear-dust). Branches of the auditory 
nerve enter the utricle and semicircular canals and are thus 
affected by any vibrations which occur in the contained fluids, 
