. The causes and course of organic evolution; . — dn. Fig. 16—a (to left) cerebral organ of Drepanophorus compared as an audi-tory organ with h (to right), the young auditory organ of mammal, o, o openor closed external orifice; du. coch. ductus cochlearis; s. u. ca. sacculo-utricularcanal; utr. utriculus; sac. sacculus; d. n., v. n. dorsal and ventral auditory nerves;du. endo. ductus endolymphaticus. It is now well recognized that the ear is innervated by twodistinct branches of the auditory nerve, and that it performsa double function. The cochlear branch, distributed
. The causes and course of organic evolution; . — dn. Fig. 16—a (to left) cerebral organ of Drepanophorus compared as an audi-tory organ with h (to right), the young auditory organ of mammal, o, o openor closed external orifice; du. coch. ductus cochlearis; s. u. ca. sacculo-utricularcanal; utr. utriculus; sac. sacculus; d. n., v. n. dorsal and ventral auditory nerves;du. endo. ductus endolymphaticus. It is now well recognized that the ear is innervated by twodistinct branches of the auditory nerve, and that it performsa double function. The cochlear branch, distributed to thecochlea and ampullae of the ear, enables the latter to perceivesounds; the vestibular branch that passes to the semicircularcanals has for function the maintaining of equilibrium, or,as we would suggest, is geoperceptive or geotactic. Evolution of Animals 431 In Cerehratidus, as described and figured by Burger, theexternal orifice, the ciKated canal, the two diverticula, andthe distinct nerve branches seem well to correspond to theear orifice, the ciliated lym
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