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 . e isas hidden and mysterious and impalpable as the na-ture of our consciousness. Let us now examine thestructure of the organ which perceives this strangestimulus and enables it to affect our brain. 373. Situation of the Eye.—The eye is situatedin a cavity called the orbit, surrounded by bone ex-cepting in front, and padded all about
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 . e isas hidden and mysterious and impalpable as the na-ture of our consciousness. Let us now examine thestructure of the organ which perceives this strangestimulus and enables it to affect our brain. 373. Situation of the Eye.—The eye is situatedin a cavity called the orbit, surrounded by bone ex-cepting in front, and padded all about with fattyand muscular tissues, so that, although it is pro-tected from injury by an unyielding bony case, itstill reposes on a soft and elastic bed. 374. Structure of the Eyeball. — The eyeball(Fig. 66) is nearly spherical, and about an inch indiameter. It is formed of three membranes, ar-ranged concentrically one within the other, and theinterior is filled with certain structures necessary tovision. The outer membrane is called the sclerotic^ * Scleratic, from the Greek (TKAripds, Aard, because it is the hardestand toughest coat of the eye. SIGHT, 293 coat, and in front, where it is visible, constituteswhat is commonly known as the white of the Fig. 66.—Horizontal section of the right eje, showing the relative poshion of its parts. It is composed of white, fibrous tissue, and is ex-ceedingly strong, tough, and elastic. It surroundsthe whole eyeball, excepting in front, where a trans-parent membrane, about ^th of an inch thick, is setinto it like a watch-s^lass in the case. The front ofthe eye must of course be transparent for the ad-mission of light. This portion of the eye is calledthe cornea:^ * Cornea, from the Latin cornu, a horn, because of its resemblanceto transparent 294 ORGANS OF PERCEPTION, Just inside the sclerotic coat is another coat,called the choroid,^ which covers the whole interiorof the eye, excepting that portion bounded by thecornea. T
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