. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 474 Comparative Animal Physiology to vibrate as a unit. This motion causes a rocking of the stapes, which is fastened eccentrically to the inner ear drum covering an oval window in the bony inner surface of the middle ear. There are two small muscles in the middle ear, one attached to the malleus and one to the stapes. Contraction of these muscles reduces the amplitude of the vibrations and thereby de- creases the sensitivity of the ear. Contraction is usually under reflex control, but in exceptional cases it ma
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 474 Comparative Animal Physiology to vibrate as a unit. This motion causes a rocking of the stapes, which is fastened eccentrically to the inner ear drum covering an oval window in the bony inner surface of the middle ear. There are two small muscles in the middle ear, one attached to the malleus and one to the stapes. Contraction of these muscles reduces the amplitude of the vibrations and thereby de- creases the sensitivity of the ear. Contraction is usually under reflex control, but in exceptional cases it may be voluntary. Below the oval window is another opening, the round window, which is also covered by a membrane, the auxiliary ear drum. The bones of the middle ear do not make contact with the membrane of the round window, the function of this membrane being to relieve the pressure exerted on the inner ear by the stapes. When the covering of the oval window is pushed inward by the stapes, the cover- ing of the round window bulges outward. The cavity of the middle ear is connected to the oral cavity by the eustachian tube, the function of which is to equilibrate air pressure of the middle ear with that of the environment and to serve as a drainage TYMPANIC ME Fig. 154. Diagrammatic representation of the ear. A, Schematic diagram of middle and internal ear. The oval window (unlabeled) lies above the round window and con- tacts the stapes. B, Schematic diagram of the ossicles of the middle ear, showing position of various members at rest and after inward displacement of tympanic membrane. Dotted lines and arrows represent path of sound waves. After Stevens and Davis'" from Fulton.^" The principal function of the middle ear is to transmit sound waves from air to liquid. Because of the ratio of the areas of the tympanic membrane and the stapes (90 to square millimeters) and the reduction in total am- plitude of vibration (by a factor of 2) there exists a very
Size: 2323px × 1075px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisher, booksubjectphysiologycomparative
