The
secondary tympanic membrane (or round window membrane) covers the
round window, sealing off one of two openings into the inner ear. It separates the
scala tympani of the
cochlea from the middle ear. It vibrates with opposite phase to vibrations entering the cochlea through the
oval window as the fluid in the cochlea is displaced when pressed by the
stapes at the oval window. This ensures that hair cells of the
basilar membrane will be stimulated and that audition will occur.