. The comparative anatomy of the domesticated animals. Veterinary anatomy. 950 THE SENSORY APPARATUSES. infmor is smaller, spherical in shape, and forms the sacculus; it appears to be perfectly closed, though in contact with the utriculus. The membranous vestibule is composed of two distinct layers— an external, of connective tissue ; and an internal, epithelial, resting on an amorphous mem- brane. At the expansion of the nerve-filaments, the latter is absent, and is replaced by a white calcareous substance (minute crystalline particles of carbonate and phosphate of lime) which, in the domesti
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 950 THE SENSORY APPARATUSES. infmor is smaller, spherical in shape, and forms the sacculus; it appears to be perfectly closed, though in contact with the utriculus. The membranous vestibule is composed of two distinct layers— an external, of connective tissue ; and an internal, epithelial, resting on an amorphous mem- brane. At the expansion of the nerve-filaments, the latter is absent, and is replaced by a white calcareous substance (minute crystalline particles of carbonate and phosphate of lime) which, in the domesticated animals, appears as a powder, and is named the calcareous powder of the vestibule, ear-dust, or otoconites (otoliths), (Some authorities give four layers : an external or serous, derived from the lining membrane of the laby- ^ig- 51*- rinth ; a vascular, with multi- tudes of vessels; a nervous, _ _^ formed by the expansion of the ^1^^ ^'^ .|^P2^'^--^^^^gt^l|| , filaments of the vestibular nerve ; //f '^""^ / jtV\'^^^^p^^*^^K^pff|ffif^ and an internal serous membrane, r/U P'S,'%^^mmmj^^»!m\\n\mM,/ ^^.^^^Yi secretes the limpid fluid contained in its interior. Spots of pigment are constantly found in the tissue of the membranous labyrinth.) 2. The Membranous Semicir- cular Canals (Fig. 513). These are three thin tubes, which correspond exactly with, though they are of smaller diameter than, the osseous semi- circular canals; they open into the utriculus in the same manner as the latter do into the bony vestibule. Each has one of its two extremities dilated into a sac or ampulla (sinus-ampullaceus); for the two superior and external canals it is the anterior extremity, and for the posterior canal the outer extremity. In structure they resemble the vestibular THE COCHLEA OPENED, TO SHOW THE ARRANGEMENT OF THE TWO RAMPS AND DISTRIBUTION OF THE AUDITORY NERVE. a, Cochlea; b, auditory nerve; c, blood-vessel; d, d', vascular ramifications; e, posterior part of
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