[AS.] The mechanism through which sound reaches the brain. In man and the higher vertebrates the ear is divided into three parts the outer opening, or meatus ; the middle ear, o r tympanum or drum; the inner ear, or labyrinth. The membranous labyrinth con-sists of a number of sacs and tubes containing a lymph fluid, which fills a cavity known as the bony labyrinth. The sound collected by the outer ear sets the tympanic membrane vibrating; the bones in the middle ear convey these vibrations to the inner ear, where the fibres of the auditory nerve receive them and send them to the brain. A passage called the eustachian tube opens from the inner cavity into the throat. When through cold the throat is swollen, the mouth of this tube may close and deafness ensue. The ears of animals of prey bend forward to collect the sounds in the direction of the pursuit. The ears of animals of flight, as hares and deer, turn backward to catch the sounds that may warn them of approaching danger.

Tympanum

[Gk.] The drum of the ear (q. v.)