. Animal physiology. Physiology, Comparative; Physiology, Comparative. STRUCTURE OF THE EAR IN MAN. 389 catch most advantageously the faintest sounds from any quarter. This is especially the case with animals that are naturally timorous, such as the Hare or the Deer; these have usually very large external ears. But it is among the Bat tribe,— whose residence in the dark recesses of caverns and excavations makes their eyes of comparatively little use to them, and causes them to depend greatly for guidance in their movements upon the sense of hearing,—that we find the greatest development of the
. Animal physiology. Physiology, Comparative; Physiology, Comparative. STRUCTURE OF THE EAR IN MAN. 389 catch most advantageously the faintest sounds from any quarter. This is especially the case with animals that are naturally timorous, such as the Hare or the Deer; these have usually very large external ears. But it is among the Bat tribe,— whose residence in the dark recesses of caverns and excavations makes their eyes of comparatively little use to them, and causes them to depend greatly for guidance in their movements upon the sense of hearing,—that we find the greatest development of the external -Long-eared Bat. 516. The canal (d, Fig. 193), into which the external ear collects the sonorous vibrations, passes inwards, until it is ter- minated by a membrane stretched across it, which is called the membrana tympani, or membrane of the drum of the ear (^). This forms the outside wall of a cavity excavated in the petrous portion of the temporal bone, the inner wall of which is bony, and forms the partition between the middle and internal ear. The cavity of the tympanum, constituting the middle ear, is not one of the essential parts of the organ ; for nothing analogous to it exists in Fishes, nor in the lower Reptiles. It contains air; and communicates with the back of the nasal cavity (n, Fig. 189) by a canal termed the Eustachian tube (k, Fig. 193). It is the partial or complete closure of this tube, by swelling of its lining membrane, or by the viscid secretion from it, that occasions the slight deafness common among those who are suffering from. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Carpenter, William Benjamin, 1813-1885. London : Wm. S. Orr and Co.
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