The middle ear muscle of frogs does not modulate tympanic responses to sound.

The effect of the opercularis (= middle ear) muscle on the acoustic responsiveness of the tympanic middle ear of anuran amphibians was studied using laser vibrometric measurements of tympanic responses to sound. Removal of the muscle or direct stimulation of denervated muscles had no measurable effects on tympanic responses to sound in either American bullfrogs (Rana catesbeiana) or green treefrogs (Hyla cinerea) at any frequency or at any sound-pressure level studied. These results suggest that, contrary to proposed hypotheses, the opercularis muscle of the anuran middle ear is not capable of modulating the responsiveness of the tympanic middle ear. Instead, the opercularis system most likely functions as an independent system involved in acoustic reception.