. A text-book on physiology : for the use of schools and colleges : being an abridgment of the author's larger work on human physiology. e essential portion of the labyrinth, and the semicircu-lar canals and cochlea appendices that have branchedforth from it. The vestibule and semicircular canals are lined witha membrane which, of course, copies their shape, yet itis not in contact with their bony walls, but is partedtherefrom by a stratum of water; to this the name ofperilymph is given; their interior is also filled with aliquid—the endolymph it is called. The bony structureis called the bony
. A text-book on physiology : for the use of schools and colleges : being an abridgment of the author's larger work on human physiology. e essential portion of the labyrinth, and the semicircu-lar canals and cochlea appendices that have branchedforth from it. The vestibule and semicircular canals are lined witha membrane which, of course, copies their shape, yet itis not in contact with their bony walls, but is partedtherefrom by a stratum of water; to this the name ofperilymph is given; their interior is also filled with aliquid—the endolymph it is called. The bony structureis called the bony labyrinth; this structure is the mem-branous labyrinth. A portion of the auditory nerve di-vides into three main branches, which present them-Fig. 87. selves for the supply of the ampul- lae : the brush-like terminations ofthese are accommodated with anotolith, or ear-stone. Fig. 87: a, external wall of ves-tibule, on which is seen, b, fenes-tra ovalis; c, fenestra rotunda, Tympanic face of the labyrinth. an(^ ^ tract of the facial nerve ; What are the semicircular canals? What are the perilymph andendolymph ? Describe Fig. FUNCTION OF THE SEMICIECULAE CANALS. 273 e, superior semicircular caual; y; posterior semicircularcanal; (/, horizontal semicircular canal; i % wall of thecochlea; j, aqueduct of cochlea; k, portion of petrousbone. The explanation usually given of the function of thesemicircular canals is, that they serve to determine thedirection of sounds, an idea originating from their re-markable rectangular position. However, this is ac-complished in almost all cases by directing the externalcanal toward the point from which the sound is coming,and judging of its place by the variations of its intensi-ty. Animals commonly direct the external ear towardthe sounding point, guided doubtless in the same physiologists have restricted the use of the semi-circular canals to the collection of those sounds whichstrike upon the skull, but, besides the preceding c
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