Bullfrogs (Lithobates catesbianus, formerly Rana catesbeiana) have a distinct tympanic fold that wraps around the tympanum or ear membrane. The tympanum is composed of nonglandular skin and unlike or own eardrum it is situated externally on the frog, in most species directly behind the eye. It functions in a similar fashion to our own eardrum. There is a bone attached to the tympanic membrane which also attaches to the oval window of the inner ear. When sound waves strike the membrane vibrations are transferred via this bone to the fluid of the inner ear. This in turn causes receptors within the inner ear to be stimulated, sending a transmission to the brain for processing. Range: native to all of New England except Northern Maine; introduced and becoming established west of the Rockies. Habitat: marshes, ponds, and slow rivers. Ludlow, MA.