252 The Structure of the Cochlea and the Perception of Tone 
from the deeper tones would produce vibrations in the much larger tec- 
torial membrane found in the upper coils.’ 
The vibrations in a part of the membrana tectoria produced by a par- 
ticular tone must necessarily involve a considerable area of this struc- 
ture. As a result, a more or less extensive group of hair cells is stimu- 
lated. The nerve impulses arising from the stimulation of the several 
hair cells included in this group come together in the brain center of 
the cortex, where the tone picture forms the final step in the perception 
of this particular tone. When a tone slightly higher or lower than this 
one, is produced, the same group of hair cells is stimulated, excepting 
for the addition of a few.more cells at one end and the loss of a few 
cells at the other end of the area involved. The sum total of the impulses 
which reach the center in the brain is, therefore, different for every tone, 
however near they may be in the scale. The ability to distinguish be- 
tween the several tones is, therefore, a matter of education, since anatom- 
ically we encounter no difficulty in accounting for a different tone picture 
for each particular tone difference. 
A necessary corollary of the fact that the vibration of the membrana 
tectoria resulting from a particular tone spreads over a considerable area 
of this membrane is the fact that when two tones near each other in the 
scale are produced simultaneously the two areas of the membrana tectoria 
thrown into vibration will overlap to a greater or less extent. This 
overlapping of the areas stimulated by several tones was first conceived 
by Helmholtz in his basilar membrane theory and has been looked upon 
by many as one of the strongest arguments in favor of his resonator 
hypothesis since it offers perhaps the most plausible explanation of the 
most difficult of all the secondary phenomena of tone perception to be 
accounted for, namely, the phenomenon of “ beats.” The objections to 
this ingenious conception of Helmholtz which are based on the very 
apparently rigid inflexible character of the membrana basilaris do not 
* Whether the facts which we now possess regarding the structure of the 
membrana tectoria are accurate enough to furnish the physical basis which 
will explain exactly how the membrana tectoria fills the role of resonator 
is a question for the physicist to answer. Whether or not the anatomist will 
ever be able to furnish accurate enough data regarding the structure of the 
membrana tectoria to satisfy in detail the physical requirements of a resonator, 
at least of the types of resonators now recognized by the physicists, does not 
in any way detract from the logical conclusion here reached, viz. that in the 
membrana tectoria is located the mechanism which fills the role of physical 
resonator. 
