. Human physiology : designed for colleges and the higher classes in schools, and for general reading. rove an effectual defense against direct thrusts. If the weaponhit this cartilage, it acts as a firm shield, to ward off the blowfrom the eye behind it. And even that part of the lid whichis intended by its laxness to allow free motion to the lid, theskin, is often an effectual defense. If an impending blow beseen, and the eye be instantaneously and forcibly shut, thewrinkled skin forms a soft cushion over the eye, and thus notonly covers it up, but serves materially to deaden the force ofthe
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. rove an effectual defense against direct thrusts. If the weaponhit this cartilage, it acts as a firm shield, to ward off the blowfrom the eye behind it. And even that part of the lid whichis intended by its laxness to allow free motion to the lid, theskin, is often an effectual defense. If an impending blow beseen, and the eye be instantaneously and forcibly shut, thewrinkled skin forms a soft cushion over the eye, and thus notonly covers it up, but serves materially to deaden the force ofthe blow. 473. The tear apparatusaffords the eye materialprotection. The bland tearskeep the organ properlylubricated, so that its con-stant motions occasion noirritation. And if any thinggets into the eye, the tearsare manufactured abund-antly, for the purpose ofwashing out the intrudingsubstance, which is generallyeffected. Fishes have noneed of a tear apparatus, astheir eyes are washed con-stantly by the water inwhich they live. In is represented the tear-apparatus. The tears are FIG. TEAR APPARATUS. THE EYE. 317 Tear apparatus. Oiling the eyelashes. secreted by a small gland, called the lachrymal gland, situatedat a, in the orbit under the arch of the forehead, and near theouter angle of the eye. At b are the ducts which empty thetears in upon the surface of the eye on the inside of the upperlid. By the constant motions of the organ the tears are diffusedover its whole surface, and thus continually wash the eye. Thearrangement for carrying off the fluid is this. It flows througha tube, d, e, into the nose. This tube has at its beginning inthe eye two branches, c, c, which open on the edges of the twolids at the inner corner of the eye. These open mouths, thatdrink up the tears as they flow to them, you can very readilysee. The drain of the eye, which thus conveys the to the nose, is ordinarily capable of taking care of all thetears that the gland m
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