. Elementary biology, animal and human. Biology. ADDITIONAL TOPICS IN HUMAN BIOLOGY 163 is white in color, except in front, where it becomes the transparent cornea. Inside of the outer coat is a second layer which is seen beneath the cornea as a colored ring known as the iris. In the center of the iris is a circular opening, the pu-pil, which is black in appearance. Through the pupil enter the rays of light into the interior of the eyeball. If one comes suddenly from a dark room into the light, it is possible to see this opening quickly decrease in size. The inner Uning of the eyeball is extre
. Elementary biology, animal and human. Biology. ADDITIONAL TOPICS IN HUMAN BIOLOGY 163 is white in color, except in front, where it becomes the transparent cornea. Inside of the outer coat is a second layer which is seen beneath the cornea as a colored ring known as the iris. In the center of the iris is a circular opening, the pu-pil, which is black in appearance. Through the pupil enter the rays of light into the interior of the eyeball. If one comes suddenly from a dark room into the light, it is possible to see this opening quickly decrease in size. The inner Uning of the eyeball is extremely thin and black in color; it is known as the retina, and connected with it are the many nerve fibers that carry messages to the brain. Behind the iris is a beautiful transparent object, the crystalline lens, both surfaces of which are convex. The space within the eye- ball in front of this lens is occupied by a liquid, and behind the lens is a jeUylike substance. Fig. 52. ^ Section of the eye. 245. The eye as a camera. — Any one who is at all familiar with a camera knows that by means of a lens, or a combination of lenses, the scene to be photographed is made to appear upside down on the ground glass plate at the back of the camera. If the image is not clear, it is brought into focus by moving the lens nearer to, or farther from, the object. In the eye, too, we have an arrangement similar to that of a camera, since the convex surfaces of the cornea and crystalline lens (Fig. ^3) focus the rays of light so that an image is formed on the sensitive retina at the back of the eye. Since, however, the lenses within the eye cannot be moved backwards and forwards, as in a camera, focusing or accommodation of the eye must be accomplished. C = Cornea. I = Iris. L = Cryatalline lens. ON = Optic nerve. R = Ketina. V. H. = Jellylike Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
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