Journal of morphology . canal. cp Posterior canal. / Lagena. m Mid-brain. h Hind-brain. 11 Nose. u Umbilical cord. from the sacculus, the Shark ear assumes the conditions andproportions which characterize it in the adult. The ductus en-dolymphaticus retains its connection with the exterior through-out life, and places the internal ear in communication with the No. I.] THE VERTEBRATE EAR. lyy sea-water. In many forms of Elasmobranchs the ear containsscarcely any crystals, and not unfrequently sand grains are foundwithin the ear. The sea-water undoubtedly plays a consider-able part in removing t
Journal of morphology . canal. cp Posterior canal. / Lagena. m Mid-brain. h Hind-brain. 11 Nose. u Umbilical cord. from the sacculus, the Shark ear assumes the conditions andproportions which characterize it in the adult. The ductus en-dolymphaticus retains its connection with the exterior through-out life, and places the internal ear in communication with the No. I.] THE VERTEBRATE EAR. lyy sea-water. In many forms of Elasmobranchs the ear containsscarcely any crystals, and not unfrequently sand grains are foundwithin the ear. The sea-water undoubtedly plays a consider-able part in removing the otoliths that are found in all species,by dissolving them. The mechanical forces active in the modelling of the ear arefor the most part the inherited tendencies of cell growth ac-quired as legacy from the canal organs of the surface of thebody. The other forces are the pressures due to enlargementof ear and the concomitant reduction of space in which ithas come to lie, the growth of the nerves into the ear, and the. Cut 20. — Diagram to illustrate the relations of sense organs of the ear when the earvesicle is spread upon the surface of the head. establishment of the vascular supply. The cochlear tube beginsas a straight evagination, and curves soon after it comes in con-tact with the body wall. Inherited tendencies suffice to bringabout the division of the primitive sensory area, the formationof the ampullae, and the canals, except so far as the canals havea more or less curved outline. The canals are curved for thereason that they are formed as flattened pockets given off froma curved surface, and by the fusion of the edges of the foldalong the whole mouth of the pocket, except at the two ends,where the tube thus formed opens into the utricular cavity atboth ends. More clearly to understand that this is so, supposethe auditory vesicle with canals well formed be again drawn to 1^8 A VERS. [Vol. VI. the surface of the head and caused to spread itself out flat. Theinner fa
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Keywords: ., bookauthorwistarin, bookcentury1800, bookdecade1890, bookyear1892
