EAR

the organ of hearing, is divided in man into external. middle, and internal ear. The external ear consists of two parts, the auricle, or pinna, a fibro cartilaginous framework covered with skin, the purpose of which is to catch the vibrations of the air, and the auditory meatus, a bony and in part cartilaginous canal pa ing into the temporal bone and ending at the tympanic membrane, which separates it from the middle ear. The auditory meatus is lined with skin, the glands of which secrete wax. The middle ear, or cavity of the tympanum, is a small cavity situated in the petrous portion of the temporal bone, the purpose of which is to transmit to the internal ear the sounds which strike the tympanic membrane. It is filled with air (from back of nasal cavity through Fust a chi an tube), so as to preserve uniform temperature, to increase action of the sound conveyers, and to keep pre ure equal on each side of the tympanic membrane. Between the middle ear and the internal ear are two fine membranes covering little openings called the fenestra rotunda and the fenestra oval is; and the vibrations caused by sounds are transmitted from the tympanic membrane to the membrane of the fenestra oval is, and thus propagated to the internal ear, by a chain of little bones in the middle ear, called from their shapes the malleus, incus, and stapes (2. e., hammer, anvil, and stirrup). The internal ear is composed of a series of cavities in the petrous portion of the temporal bone, comprising the vestibule, the central cavity, into the superior part of which open three canals, named from their shape the semi-circular canals, while the front part of the vestibule is prolonged into a spiral canal resembling the shell of a common snail, the cochlea. A spiral bony shelf divides the cochlea incompletely into two pa ages; an upper, or scala vestibult, and a lower, or scala tympani. Within the bony cavities is contained a series of membranous canals which closely follow them in shape, but, being much smaller in calibre, are not in close contact with their walls. Between the walls of the two series of canals is a space filled with a special fluid, the perilymph, while the membranous canals are filled with another fluid, the endolymph. In the vestibule the membranous labyrinth is divided into a small sac, the saccule, into which the membranous canal of the cochlea opens, the utricle, into which the membranous semi-circular canals open, and a slender blind canal, the endolymphatic duct. The membranous semicircular canals are only about a quarter-width of the corresponding bony canals, and at one end of each is a large dilatation, or ampulla, into which the hairs of hair-cells project. The membranous cochlea, or cochlear duct, lies in the bony canal between the free ed of the bony shelf and the outer wall, and along its base extends a minute structure, the organ of Corti, the e ential part of which consists of hair-cells projecting into the endolymph. Physiology of the Ear.—When vibrations of a body set up air-waves (which -- cause the sensation called sound) they are reflected by the external ear and pa into the auditory meatus, and strike the tympanic membrane. The vibrations are transmitted by the chain of o icles, and, the base of the stapes being attached to the membrane of the fenestra oval is, are then transferred to the perilymph. The waves in the perilymph set up corresponding waves in the endolymph, and these effect the nerve endings to the different parts. The utricle and saccule can only perceive sounds as sounds, the analysis of tone is the function of the cochlea, its hair-cells bein irritated by the waves of endolymph, an the sensation communicated to the brain by their fine nerve filaments. The function of the semicircular canals is concerned with the sense of equilibrium, the hair-cells of the ampullae being irritated by the waves of endolymph | caused by change of position.; Diseases of the Ear may affect either the external, middle, or internal ear. The auditory meatus may be impacted with wax (the commonest cause of temporary deafne ), the products of inflammation, etc., or the tympanic membrane may be thickened, have adhesions, be the subject of other diseases, or suffer from wounds caused by violence. Another common cause of deafne is the closure of the Eustachian tube at its opening into the upper part of the throat. A serious and common cause of pain in the ear is inflammation, suppurative or not, of the tympanic cavity (middle ear). This often has a discharge coming from it, and its seriousne is due to its proximity to the brain, to which inflammation may extend and cause death. As soon as po ible the ear should be syringed out with a mild antiseptic solution, and the external meatus plugged with cotton wool to dry up the moisture.: Foreign bodies in the ear can usually be removed by syringing with warm water or by dropping in warm glycerine. See Duar anp Dus, Care of.