Tympanic membrane

“ In all the Amphibia, Sauropsida and Mammalia, except the Urodela and a few Anura and Reptilia, the first visceral or hyomandibular cleft enters into intimate relations with the organs of hearing, and from it and the adjoining parts are formed the tympanic cavity, the Eustachian tube, the tympanic membrane and the meatus auditorius externus. The tympanic membrane serves to receive from the air the sound vibrations, which are communicated to fluids contained in the true auditory labyrinth by one ossicle or by a chain of auditory ossicles. ”

“ Such growths, provided they are pedunculated and do not abut on the tympanic membrane, can sometimes also be removed by the same method; much depends on their shape and situation. If sessile or too deeply placed, the operation may have to be completed by reflecting forward the auricle. Before terminating the operation a clear view of the tympanic membrane should always be obtained.
The meatus is finally syringed out with a 1 in 5,000 aqueous solution of biniodide of mercury and dried, a strip of sterilized gauze being inserted into the auditory canal. ”

“ The tympanic membrane is furthermore able to render sensible differences in the pressure of the external atmosphere, too slight to be felt either as noise or in this more violent way. If the reader will sit with closed eyes and let a friend approximate some solid object, like a large book, noiselessly to his face, he will immediately become aware of the object's presence and position—likewise of its departure. ”

“ With successive sharp taps of the mallet, the gouge is made to cut through the pedicle, care being taken that the instrument is not driven in too deeply, on to the tympanic membrane.
The growth, which can now be felt to be movable within the meatus, can usually be removed by grasping it between the blades of forceps, or can be expelled by syringing the ear. After its removal the auditory canal should be plugged for a few minutes with a solution of cocaine and adrenalin chloride. ”

“ The instrument of hearing in man consists of an external orifice about an inch and a half deep in adults, which is closed at the bottom by the circular tympanic membrane. This membrane, though moderately strong, is quite thin, and almost transparent. ”

“ The perforation in the tympanic membrane becomes smaller, and often entirely closes, so that in a young person the restoration may be so complete that it is difficult to know where the seat of perforation has been. ”

“ Generally speaking, very high tones are heard more easily than low tones of the same intensity. As the membrana tympani is not only fixed by its margin to a ring or tube of bone, but is also adherent to the handle of the malleus, which follows its movements, its vibrations meet with considerable resistance. This diminishes the intensity of its vibrations, and prevents also the continued vibration of the membrane after an external pressure has ceased, so that a sound is not heard much longer than its physical cause lasts. ”

“ It has always been regarded as one of the mysterious miracles of vital structure how the little membranous drum of the human ear can take up so perfectly this rapid stream of intricate motions in the air, which are all so exactly reproduced by the layer of adjacent particles striking upon the membrane, that thousands of tympanums will be all affected precisely alike, while the nerves transmit the thrills to the brain, awakening the same musical sensations and sentiments in the consciousness of as many people as can be brought within hearing. ”

“ When sound-waves strike the tympanum, they cause it to move inwards and outwards in a series of rapid movements. The ossicles operated by the tympanum press on the little opening O, covered by a membrane, and every time they push it in they slightly squeeze the perilymph, which in turn compresses the endolymph, which affects the nerve-ends, and telegraphs a sensation of sound to the brain. ”

“ If this process is going on in the same medium (the air) in which our ear is situated, the membrane will at every condensation be forced toward the hollow of the drum, and at every rarefaction will move itself in the opposite direction.
These vibrations necessitate a similar motion of the auditory ossicles, and thereby a transference to the auditory nerves is effected.
The greater the condensation of a sound-conducting medium at any given moment, the greater also will be the amplitude of vibration of the membrane and of the auditory ossicles and of their action ”

“ Across the end of this canal, a membrane or skin called the tympanum is stretched, like the parchment over the head of a drum, and it is this membrane which moves to and fro as the air-waves strike on it. A violent box on the ear will sometimes break this delicate membrane, or injure it, and therefore it is very wrong to hit a person violently on the ear. ”

“ It is easily appreciable that a gradual thickening of this mucous membrane would result in a progressive impairment of the sound-transmitting apparatus, with a corresponding decrease in its power of transmitting sound waves not only from without inward but from within outward. ”