. An elementary course of practical zoology. Zoology. SENSORY ORGANS 449 olfactory nerves and is raised up into ridges So as to increase the surface. The structure of the eye, as well as of the accessory apparatus in connection with it, is in all essential re- spects the same as in the frog (p. i8i), except for the differences in the eyelids (pp-S and 410), the absence of a lachrymal apparatus (p. 186), and for the fact that the four recti muscles (Fig. 117) do not en- sheath the optic nerve, which emerges into the orbit a short dis- tance in front of their point of origin. The membranous laby
. An elementary course of practical zoology. Zoology. SENSORY ORGANS 449 olfactory nerves and is raised up into ridges So as to increase the surface. The structure of the eye, as well as of the accessory apparatus in connection with it, is in all essential re- spects the same as in the frog (p. i8i), except for the differences in the eyelids (pp-S and 410), the absence of a lachrymal apparatus (p. 186), and for the fact that the four recti muscles (Fig. 117) do not en- sheath the optic nerve, which emerges into the orbit a short dis- tance in front of their point of origin. The membranous labyrinth of the ear (compare Fig. 59, p. 187) is also very simi- lar to that of the frog, but being larger, an4 the auditory capsules being composed en- tirely of cartilage, it can be dissected out with comparative ease by slicing away the capsule with a Fig. 117.—Semidiagrammatic figure of the eye- muscles and their nerves of an Klasmobranch. ///. oculomotor, IV. pathetic, and VI. abducent nerve ; e. r. posterior rectus muscle ; i. o. in- ferior oblique ; in, r. inferior rectus ; i. r. anterior rectus ; ( of orbit; J. o. superior oblique ; j. r. superior rectus. (From Parker and Haswell's Zoology.^ A tube given off from the sacculus, called the endolymphatic duct (Fig. 59), which in the frog communicates with the lymphatic system, opens to the exterior on the top of the head in the dogfish, and thus the endolymph is in free communication with the surrounding sea-water. As we have seen, the membranous labyrinth is the essential part of the ear, and it, together with its enclosing capsule, is often spoken Pbact. Zool. G G. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Parker, William Newton, joint author. London, Macmillan and Co. , Limited; New
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