Hearing

Abstract

This chapter discusses the hearing mechanism in land and aquatic mammals. Animals use sound and hearing for communication, especially signaling different behaviors related to reproduction, breeding, territory marking, as well as for detection and localization of prey and predators and navigation. Cetaceans have succeeded superbly in aquatic hearing and have also become crucially dependent on their hearing while adapting to the aquatic world. Pinnipeds are dependent on their audition in both air and water, and their requirement to hear in both media poses demands beyond those on the whales and manatee ear. In a mammal ear, sound is collected by the outer ear pinna and guided through the external auditory meatus to the tympanic membrane, which then vibrates. These vibrations are carried further by the ossicular chain, situated in the middle ear cavity and consisting of three small bones, the malleus, incus, and stapes. The malleus is attached to the tympanic membrane with its handle, the manubrium. The middle ear ossicles together form a swing that vibrates between the tympanic membrane and the oval window of the cochlea, setting the inner ear fluid into motion. The tympanic bone and the periotic bone have several contacts with each other and are also in close contact with the squamosum and other skull bones.