諸種脊椎動物聴器の計測的研究

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The author made measurement of diameter, area and weight of the tympanic membranes, audi-tory ossicles, oval and round windows in 35 vertebrates (3 amphibians, 5 reptiles, 6 birds, 21 mammals), and examined the relationship among the measurements.The conclusions were as follows:1) The tympanic membrane in amphibia and reptile was large and variable in size in propor-tion to the size of the head. But in mammal and bird, the difference of size of the tympanic membrane between large ones and small ones was less remarkable.2) Ratio of the largest and smallest diameter of the tympanic membrane was the largest in bird, the tympanic membrane being the most elliptical in shape.3) Apex angle of the tympanic membrane was from 97 degrees in Barbary sheep to 135 degrees in mole and squirrel in mammals, and 130-165 degrees in birds. In ungulates and carnivores, of which the tympanic membranes sunk forming acute angle, handle of the malleus was generally longer compared with diameter of the tympanic ring. In other animals like horse, rodentias and birds, in which apex angle was obtuser, the " unbo " located near the center of the tympanic membrane.4) Especially broad Schrapnells membranes were noticed in some ungulates as sheep, antelope, kyon and Barbary sheep.5) Ratio of weight of the malleus to that of incus was from 4.5 to 0.84. In mammals, the malleus was heavier than incus except monkey, ox and horse. In those animals which had relati- vely small incus, the folianous process of the malleus was large, and angle of the handle of the malleus to the probable axis of rotation of the ossicular chain was small, for exampe, 13°in mole, 20°in bear, 22° in dog and 23° in bat. If the lever ratio is constant and the angle is small, the long process of the incus may be possible to become smaller, consequently the mass of the ossi-cular chain may become smaller.6) Lever ratio of the ossicle in mammal measured on the projected picture was from 1.5 to 3.2. It was generally larger than that of human and supposed to be important for the transformer action.7) Weight of the columella of bird per 1mm2 of tympanic membrane was the lightest (0.021-0.015) in vertebrates; therefore, it is suitable for the columella to move simply in and out like piston. The columella of amphibia or reptile was heavier than that of bird. In mammals, the auditory ossicles of small animals were not only absolutely but relatively light and slender, profitably lessening mass of the auditory organs.8) The round window was always larger than oval window except in man, monkey and mole, Especially in those animals which live in the water, ratio of area of both windows was large. In bird, however, the ratio was close to 1.0, both windows being almost equal- in size.9) In amphibia and reptile, ratio dividing the area of the tympanic ring by that of the ovalwindow varied range from 6 in toad to 58 in bull-frog. In bird, this ratio was constant (15-19), and similiar to that of mammals. In mammals, the ratio was from 11 to 36. Carnivoras and rodents showed big ratio.10) It is thought that auditory organ of the animals which live in the water like fur-seal, sea-lion, otter and whale, are not to be suitable for the perception of air conducting sound, because of their little tympanic membrane, little transformer ratio and narrow external meatus, having been changed to the condition which is efficient to receive the born conduction sound.
社団法人日本耳鼻咽喉科学会の論文

諸種脊椎動物聴器の計測的研究

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