. Principles of zoölogy : touching the structure, development, distribution, and natural arrangement of the races of animals, living and extinct with numerous illustrations : Part 1, Comparative physiology : for the use of schools and colleges. tympanum or drum, (c;)though it still communicates with the open air by meansof a narrow canal, called the Eustachian tube, (i,) whichopens at the back part of the the interior of the chamber arefour little bones, of singular forms,which anatomists have distinguishedby the names of malleus, (Fig. 20, c,)incus, (?z,) stapes, (5,) and os orbicUla
. Principles of zoölogy : touching the structure, development, distribution, and natural arrangement of the races of animals, living and extinct with numerous illustrations : Part 1, Comparative physiology : for the use of schools and colleges. tympanum or drum, (c;)though it still communicates with the open air by meansof a narrow canal, called the Eustachian tube, (i,) whichopens at the back part of the the interior of the chamber arefour little bones, of singular forms,which anatomists have distinguishedby the names of malleus, (Fig. 20, c,)incus, (?z,) stapes, (5,) and os orbicUlare, {o;) which are articulated to-gether, so as to form a continuouschain, as here represented, magnified. 96. The internal ear, which is ^^* also denominated the lahyrintli, is an irregular cavity formedin the most solid part of the temporal bone, beyond fnechamber of the middle ear, from which it is separated by abony partition, which is perforated by two small holes, called,from their form, the round and the oval apertures, the fora-men rotundum, (Fig. 19, g,) and the foramen ovale, (A.) Thefirst is closed, by a membrane, similar to that of the tympa-num, while the latter is closed by the stapes, one of the littlebones n the 58 SPECIAL SENSES. 97. Three parts to be distinguished in the labyrinthjnamely, the vestihule, which is the part at the entrance of thecavity; the semicircular canals^ (d,) which occupy its upperpart, in the form of three arched tubes; and the cochlea,which is a narrow canal placed beneath, at the lower partof the vestibule, having exactly the form of a snail-shell, (e.)The entire labyrinth is filled with a watery fluid, in whichmembranous sacs or pouches float. Within these sacs, theauditory nerve (f) terminates. These pouches, therefore,are the actual seat of hearing, and the most essential partsof the ear. The auditory nerve is admitted to them by along passage, the internal auditort/ canal. 98. By this mechanism, the vibrations of the
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