214 
THE EAR AND HEARING. 
represented by its separate nerve fibre. Tims it is thought 
the fibres of Corti are like timing forks, set vibrating each 
by a particular sound wave, and that each affects a particular 
fibre of the cochlea nerve only. It must be understood, 
however, that this explanation is only hypothetical, and 
still awaits definite proof. 
It will be seen that two of the cochlear scalse receive 
vibrations directly from the vestibule, viz.: the scala vestibuli 
from the perilymph, and the scala media from the endolymph. 
The scala tympani has been supposed by some to receive 
vibrations through the fenestra rotunda directly from the 
tympanum ; whilst by others it is thought more likely that 
vibrations descend it after having passed the scala vestibuli. 
I should conclude that it is affected in both these modes, 
though but slightly by the first. 
The auditory nerve, called from its softness the portio 
mollis of the seventh pair, is marked by the fineness of its 
component fibres. It enters the labyrinth by the internal 
meatus, where it subdivides into two branches, one supplying 
the vestibule, and the other forming the cochlear nerve. The 
ultimate terminations of the nerve-fibres in the cochlea have 
not yet, I think, been definitely traced, though it is almost 
certain that some of them end in the organ of Corti. 
Having now sketched the anatomy of the organ of 
hearing, it remains for us to consider a little more in detail 
some parts of the physiology of hearing not noted in connec¬ 
tion with the foregoing anatomical considerations. According 
to popular conception the pulsations of air upon the tympanic 
membrane are the necessary antecedents of sensations of 
sound ; but this appears to be disproved by the following :— 
A drum is silent if the skin be burst, because the skin is its 
only effective vibrating surface ; but the tympanum is not 
properly a drum, inasmuch as its membrane may, according 
to Cheselden, be burst, not only without destroying hearing, 
but even in some cases with a terrible increase in susceptibilty 
to sounds. Cheselden destroyed the membranes in dogs, and 
found that they were terrified at all loud sounds; and there 
is a case on record of a man with a hole in his tympanum, to 
whom the whistling of another man in an adjoining room 
was intolerable (G. H. Lewes). 
Still it is clear that the vibrations of the tympanic 
membrane are of great assistance in hearing, as it is found 
that a thickening, or stiffening of it, or even unusual dryness, 
will render hearing dull. Many a temporary deafness has 
been removed by well syringing the ear with warm soap and 
water (although in such cases the removal of indurated wax, 
