Dimensions of and vibrations in the round window membrane in cats

The shape and size of the round window membrane and its vibratory pattern were investigated in cats by use of an optical displacement meter and time-averaged holography. The round window membrane is convex toward the scala tympani and appears to be almost elliptic in shape. The major and minor axes of the membrane are 2,273 and 1,934 microns. The mean degree of convexity is 1,975 microns. Under vibration the area of maximum displacement occurs anteriorly-superiorly at low frequency. As frequency is increased, the maximum displaced area shifts posteriorly-superiorly, then breaks up into several segments.