Ear

(er) [ME., ere, ear]. The organ of hearing, consisting of the external ear, the middle ear or tympanum, and the internal ear or labyrinth. The outer ear is made up of an expanded portion, the pinna, and the external auditory canal. The middle consists of the tympanum, with the ear o icles, the Eustachian tube, and the mastoid cells. The tympanum is lined by mucous membrane, and communicates with the pharynx by means of the Eustachian tube. It is divided into three parts, the atrium, the attic, and the antrum. Its outer end is closed by the tympanic membrane, from which sound is conducted along the ear-o icles (the malleus, incus and stapes) to the fenestra oval is, which communicates with the vestibule of the internal ear. By means of the fenestra rotunda, which is closed by the entotympanic membrane, it communicates with the cochlea of the internal ear. The mastoid cells, which are also part of the tympanum, are air-spaces ch275.xhtml d 250