Fig. 11. Diagrammatic representation of the ossicular apparatus of the bullfrog showing hypothetical modes of motion. The predicted horizontal position of the `extrastapes axis' is indicated in each case with a dashed line. In A, the extrastapes and pars media are stiffly connected and all rotation is about the footplate axis. In B, there is both rotation around the footplate axis and relative movement between the pars media and extrastapes. The extrastapes axis is predicted to lie somewhere between the footplate axis and the extrastapes/pars media articulation. This is the case in the intact frog ear. In C, movement is entirely restricted to rotation at the extrastapes/pars media articulation. There is no movement of the footplate. The middle ear approaches this condition when the ascending process (not shown) is severed. Amplitudes of motion are greatly exaggerated for clarity.

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