THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

10.1 Human Hearing 215Figure 10.2. The membranous semicircular canals showing the cristae within theampullae. (From “The Internal Ear,” What’s New, 1957, Abbot Laboratories. Reproducedwith permission of the publisher.)37 mm in length that connects the middle-ear cavity with the pharynx at the rearof the nasal cavity.Just below the oval window lies another connection between the middle andinner ears, the membrane-covered round window. Between the oval and roundwindows is a rounded osseous projection, formed by the basal turn of the cochlea,called the promontory. A canal encasing the facial nerve is situated just above theoval window.The structures to the right of the oval and round windows shown in Figure 10.1are collectively called the inner ear (also called labyrinth), which comprisesa number of canals hollowed out of the petrous portion of the temporal bone.These interconnecting canals contain fluids, membranes, sensory cells, and nerveelements. Three principal parts exist in the inner ear: the vestibule (an entrancechamber), the semicircular canals, and the cochlea. The vestibule connects withthe middle ear through the oval and the round windows. Both of these windows areeffectively sealed, by the action of the stapes and its support on the oval windowand the presence of a thin membrane in the round window, thus preventing theloss of the liquid filling the inner ear. The semicircular canals play no role in theprocess of hearing but they do provide us with a sense of balance. The cochlea,