A circular tympanum near the eye of a male North American bullfrog
The tympanum is an external hearing structure in animals such as frogs, toads, insects, and mammals, to name a few.
In frogs and toads, it is located just behind the eye. It does not actually process sound waves; it simply transmits them to the amphibian's inner ear, which is protected from water and other foreign objects.
See also 
- ^ Phil Bowles. "Glossary". The Online Field Guide. Retrieved March 8, 2012.