George E. Shambaugh 2538 
hold when the delicate film-like, semi-fluid membrana tectoria takes the 
role of resonator. 
Again, the peculiar alterations in the function of hearing which occur 
as the result of pathological changes in the cochlea, find a more ready 
explanation on the hypothesis that the membrana tectoria is the resonator 
than that the membrana basilaris fills this réle. 
In the first place, the occurrence of “ tone islands,” that is, the preser- 
vation of certain circumscribed areas of hearing in cases where there has 
been more or less extensive destruction of hearing, finds as ready an 
explanation with the membrana tectoria as resonator as when we attri- 
bute this function to the membrana basilaris. 
In the second place, the explanation of the pathological phenomenon 
known as “ diplacousis binauralis dysharmonica,” where the patient hears 
a tone in the affected ear of a pitch different from that heard in the 
normal ear, is much more readily accounted for on my hypothesis. This 
peculiar phenomenon is readily explained as due to some slight alteration 
in the delicate and easily disturbed membrana tectoria which causes it 
to respond over a certain area to impulses of a different pitch than when 
in the normal condition. 
Finally, an explanation of “ tinnitus aurium™” or subjective noises may 
possibly be found in this conception of the structure and function of 
the membrana tectoria. In the first place, the character of tinnitus 
aurium is usually that of an indefinite sound like the wind in the forest 
or the rushing of water, sounds made up of a great complexity of tones 
and with no definite pitch. Clinically, these subjective sounds arise 
from a variety of pathological conditions. One of the best known causes 
of tinnitus is pressure applied to the conducting apparatus so as to push 
the foot plate of the stapes into the oval window. ‘This results in tin- 
nitus aurium of the indefinite character described above. What actually 
takes place when the stapes is thus forced into the oval window is an 
increase in the pressure of the intralabyrinthine fluid. The result of 
this alteration in pressure must be a disturbance of the membrana tec- 
toria which has apparently the same specific gravity as the endolymph 
when the latter is under its normal pressure. The hairs from the hair 
cells, as I have shown above, normally penetrate into the lower surface of 
the membrana tectoria. Any disturbance in this membrane, however 
slight, would, therefore, alter the normal relations existing between the 
membrane and the hair cells. It seems that such an alteration from the 
normal relation between membrana tectoria and the hairs of the hair 
cell§ would constitute a stimulation of these cells. When the foot plate 
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