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Fig. 6. Diagrammatic representation of the movements of the stapes and operculum of
the bullfrog at low frequencies. The operculum is portrayed as semitransparent
to reveal the flange of the pars interna underneath. In this example, when the
pars media is pushed down, which happens when the tympanic membrane is
inflected, the footplate is moved out of the oval window. As a result of the
coupling between the footplate and operculum, the operculum also moves
outwards. Note that the stapes is hinged ventrolaterally but the operculum is
hinged dorsomedially.