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Ears

A bony structure of the middle and inner ear, the auditory bulla, is composed of two compact and dense bones (the periotic and tympanic). It is housed in a cavity in the middle ear; in all toothed whales, with the exception of sperm whales, this cavity is filled with dense foam and completely surrounds the bulla, which is connected to the skull only by ligaments. This may isolate the ear from sounds transmitted through the bones of the skull, something that also happens in bats. Baleen whales have exceptionally thin, wide basilar membranes in their cochleae without stiffening agents, making their ears adapted for processing low to infrasonic frequencies.