EAR I AS. Tare. ( ()Church Slay. twho, Lith. ansir. Lat. canis, Gk. ots. of hearing as it exist, in man sod the mammalia. It is composed of three parts: the external ear. the middle ear or tynt and the internal ear or labyrinth.
Tut: EXTERNAL EAR. Th I- c011-i.ts of two portions. the auricle or Minna (the part popu laxly recognized as the ear), and the auditory canal or external auditory meatus. The auricle, on it., outer or more exposed surface, presents various eminence- and depressions. resulting from the form of its ea rtilaginnii: framework.
The. rim. called the helix. inclose% a narrow groove —the fossa of the helix —of which the inner hound a ry is a longi tudinal ridge, parallel to the helix, and known as the antilielix: usually the anti helix is divided above into two ridges inclose a shallow depression termed of the autibelix. The large (Tiaral hollow containing in its bottom the opening of the auditory canal is called the eonelta. In front of the external auditory meatus there is a pointed directed backward and known as the tragus: corresponding to this is the similar process behind the ineatu, and pointing for termed the ant itra glts. The lowest and pendulous portion of the auricle is called the The intrinsic muscles of the auricle are. in man. functionless. Resides these there are three. extrinsic muscles. passing from the adjacenPpor thins of the scalp to the ear: they are the tolbms :Jure)». attrallens Annan. and retrahens ?urent: they are rudimentary in man, though oc casional individuals are able to eontract them and thus perform perceptible movements of the car at will.
auditory canal is -lightly arched and passes inward and a little forward from the cmicha to the tympanum: it is about inehes long: at its outer end there are a number of ceruminons glands. which furnish an adhesive, -,•11,ov. and bitter substance, the earwax (see ), which serves to protect the ear from insects. ete. The coital is partly
cartilaginous and partly osseous: the osseous portion in the fodits of a bony ring. across which the dnun-membrane is stretched, and in many animals remaining persistently as a separate bone. The entire canal, a- well as the outer surface of the drum-membrane, is lined with skin.
Tilt: MIDDLE EAR. This is a small. irregular in the temporal h.mr, lined with a mucous membrane. the epithelium of which is ciliated like that of the Eustachian tube and pharynx, with NV hiCh it is dt contains three 0—ides—the 'milieus ( hammer), ill ens (anvil). and stapes(stirrup) — joined 4 by ligaments to form a small chain at tached to its outer end, by the handle of the t he 41 rum-membrane, and at its inner end, by the base of the stapes, to the membrane covering the &last ra °rails. The muscles of the middle ear are the t,nsor tympani and the stapedius. The former arises from the under surface of the por tion of the temporal bone and is inserted into the handle of the maileus. The latter takes its origin from the hollow conical eminence, termed the pyramid, which lies behind the frimstra ()cubs, and is inserted into the neck of the -tapes: by pulling the reek backward it probably compresses the contents of the vestibule. The Eustachian tube, into which the tympanic cavity opens anteriorly, is about an inch and a half it. length, and passes downward. forward, and inward to it- opening in the pharynx. It is partly bony, but chiefly cartilaginous. It serves for the escape of mucus from the middle ear into the pharynx; also by allowing free passage of air in and out of the tympanum it renders the pressure upon the inner surface of the drum membrane equal to the atmospheric pressure upon its outer surfing?. Upon the inner wall of the tympanum there arc two openings: the f. oratis, mentioned above. leading into the vestibule: and the fcnestra rotunda, covered by a membrane, leading into the cochlea.