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Oval and round windows.

Hello Lawrence and List,

(I tried to send a private answer, but it came back with a 
"bad address" notice).

The oval window is almost completely covered by the stapes 
footplate, which has an oblong shape.

A fairly wild guess on a possible advantage of that shape:

The long axis of the ellipse formed (approximately) by the rim 
of the oval window is approximately horizontal (if the person 
stands or sits). I now make the unfounded assumption that 
the two ends of that long axis do not have the same distance 
from the BM (which begins inside of the labyrinth, between 
the two windows). 

At low sound frequencies, the stapes footplate probably 
stays parallel to itself during its vibration. 

At high sound frequencies, the trajectories of the liquid 
particles just inside of the oval window are circular. 
The radii of these circles are comparatively large near the BM, 
and decrease if the distance of the considered liquid particle 
from the BM increases. (That behaviour is similar to that of
"ordinary", i.e., non-tsunami, surface waves on lakes and
oceans). The vibration of the stapes footplate may adapt itself, 
i.e. be strong close to the BM and weaker at the other end.

The human BM at its beginning is only about 0.15 mm wide.
The high-frequency vibrating-liquid region is therefore
narrow, so that a narrow stapes footplate is advantageous.
A greater dimension of the stapes perpendicular to the BM is 
good because it leads to a large vibrating area at low 

With best wishes,

Reinhart Frosch.

Reinhart Frosch,
Dr. phil. nat.,
r. PSI and ETH Zurich,
Sommerhaldenstr. 5B,
CH-5200 Brugg.
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .