The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . headtoward the eyes. 388. The Tears.—In order to keep the corneaperfectly smooth and transparent, and to preservethe softness of the mucous membrane lining the in-terior of the lids, which continually sweep over thecornea, and if rough would irritate and ruin it, aspecial fluid is provided, called the tears, which arecontinually secr
The outlines of anatomy, physiology, and hygiene Being an edition of The essentials of anatomy, physiology, and hygiene, rev to conform to the legislation making the effects of alcohol and other narcotics upon the human system a mandatory study in public schools . headtoward the eyes. 388. The Tears.—In order to keep the corneaperfectly smooth and transparent, and to preservethe softness of the mucous membrane lining the in-terior of the lids, which continually sweep over thecornea, and if rough would irritate and ruin it, aspecial fluid is provided, called the tears, which arecontinually secreted, and keep those parts constant-ly moist. The gland which provides the tears,called the lachryinalgland {Fig. ^2), is situated insidethe orbit, just above and outside of the eyeball, andits secretion is poured out on the eve by severallittle openings at the upper part of the upper lid,on its inner surface. By the winking of the lids,which occurs frequently and is usually involuntarv,it is spread over the surface of the eve. On theedge of the lids, near the inner angle of the eye,may be seen two minute openings, one in each lid. 3o6 ORGANS OF PERCEPTION. These are the mouths of two little canals, whichpass from these points toward the nose, soon unit-. FiG, 72.—Left eyelids from behind. Above and at the left is the lachrymalgland. On the lids are seen what look like strings of beads. They areglands that secrete the fatty matter that coats the edges of the lids, andkeeps the tears from running over. ing in one larger canal, which runs downward intothe nasal cavity. Through these minute canals, thesuperfluous tears run off into the nose. Thesecanals are lined with mucous membrane, and, dur-ing a cold in the head, the inflammation often closesthem, and the tears, not finding free passage throughthem, overflow upon the cheeks. This overflowalso occurs when from pain or any powerful emo-tion the tears are increased in amount so that thecanals are unable to dispose of the extr
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