. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. HEARING. 569 municate vibrations ia the invertebrates. When the cephal- opod moUusks, with their highly developed nervous system, are reached, we find a membranous and cartilaginous labyrinth. Among vertebrates the different parts of the mammalian ear are found in aU stages of development. The outer ear may be wholly wanting, as in the frog, or it may exist as a meatus only, as in birds. The tympanic cavity is wanting in snakes. Most fishes have a utricle and th
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. HEARING. 569 municate vibrations ia the invertebrates. When the cephal- opod moUusks, with their highly developed nervous system, are reached, we find a membranous and cartilaginous labyrinth. Among vertebrates the different parts of the mammalian ear are found in aU stages of development. The outer ear may be wholly wanting, as in the frog, or it may exist as a meatus only, as in birds. The tympanic cavity is wanting in snakes. Most fishes have a utricle and three semicircular canals, but some. Ftg. 415.—Auditory vesicle of a heteropod mollask (Pterotrachea) (after ClauB). ilT, auditory nerve; Oi, otolith in fluid of vesicle; Wz, ciliated cells on inner wall of vesicle; Hz, auditory cells; Cz, central cells. have only one ; and the lowest of this group have an ear not greatly removed from the invertebrate type, as may be seen in the lamprey, which has a saccule with auditory hairs and oto- liths, in communication with two semicircular canals. Most of the amphibia are without a membrana tympani. The frog has (1) a membrana tympani communicating with the inner ear by (2) a bony and cartilaginous lever (columella auris), and (3) an inner ear consisting of three semicircular canals, a saccule and utricle containing many otoliths, and a small dilatation of the vestibule, which may indicate an undeveloped cochlea. The membranous labyrinth is contained in a periotic capsule, partly bony and partly cartilaginous, which is supplied with. 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 Mills, Wesley, 1847-1915. New York, Appleton
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