. Un testo-libro di fisiologia comparativa per gli studenti e i professionisti della medicina comparativa (veterinaria) . s thatthe orbicularis guida il fluido direttamente attraverso i tubi, keptopen da disposizioni muscolari ; e ci sono diverse opinioni divergenti. La prevenzione di verricello porta ad irritazioni dell'occhio, Che può assumere un carattere serio, così thatthe evidente uso della secrezione di tearsis per mantenere l'occhio sia umido che pulito.benchè rudimentale nell'uomo, quindi in tutti i nostri animali domestici un thirdeyelid {membrana nettitans) che può essere fatto spazzare sopra l'occhio e così purificarlo

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. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . s thatthe orbicularis drives the fluid directly through the tubes, keptopen by muscular arrangements ; and there are several otherdivergent opinions. The prevention of winking leads to irrita-tion of the eye, which may assume a serious character, so thatthe obvious use of the secretion of tearsis to keep the eye both moist and clean.Though rudimentary in man, thereis in all our domestic animals a thirdeyelid {membrana nictitans) whichmay be made to sweep over the eyeand thus cleanse it. It is especiallywell developed in those groups ofmammals that can not derive assist-ance in wiping the eyes from their fore-limbs, hence is found in perfection insolipeds and ruminants. It is made upof a fibro - cartilage, prismatic at itsbase, and thus anteriorly where it iscovered by the conjunctiva. It is mostattached at the inner can thus of theeye, from which region it can spreadover the whole globe anteriorly. The fibro-cartilage is con-tinued backward by a fatty cushion which is loosely attached. Fig. 398.—Lachrymal canals, lachrymal sac, and nasalcanal in man opened fromthe front (after Sappey.). VISION. 551 to all the ocular muscles. When the globe of the eye is with-drawn by its muscles, the third eyelid is pushed out in a me-chanical way with little or no direct assistance from muscles. In this connection may also be mentioned the gland ofHarder, a yellowish red glandular structure situated about themiddle of the outer surface of the third eyelid, which furnishesa thick unctuous secretion, also of a protective character. Thesestructures are all the more necessary, as in few animals is theglobe of the eye so well protected by bony walls as in man. SPECIAL CONSIDERATIONS* Comparative.—It seems to be established that some animalsdevoid of eyes, as certain myriopods, are able to perceive thepresence of light, even when the heat-rays are cut off. The mostrudimentary

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• bookcentury1800
• bookdecade1890
• bookpublishernewyo
• bookyear1890