File:Anatomy, physiology and hygiene for high schools (1900) (14781202482).jpg

Identifier: anatomyphysiolo00hewe (find matches)
Title: Anatomy, physiology and hygiene for high schools
Year: 1900 (1900s)
Authors: Hewes, Henry Fox, 1867-
Subjects: Physiology Health education (Secondary) Human anatomy
Publisher: New York : American Book Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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pressions of light, which come froin with-out through the pupil and lens, on to the brain in such a waythat we get there an image of the thing before our eyes.- These stru(^tures which receive the light impressions areknown as the rods and cones. Over the whole surface of theretina is a layer made up of numerous rodlike cells, withtapering threadlike processes running toward the front ofthe eye, and of sugarloaf-shaped bodies with short processes,the cones. The processes of both rods and cones give outdelicate threads which run to cells deeper in the retina, andthese again attach to the fibers of the nerve. The structuresof the retina are laid down in eleven layers. The nervelayer is in front. The light passes in through all thesestructures to the layer (^f rods and cones. Here the im-pression is taken and the cell processes set vibrating. This THE SPECIAL SENSES 247 vibration is transmitted from the rods and cones to thenerve fibers, and thns to the brain« Outer or churuidal surface
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I, Layer of pigment cells 7 ( aycr of rods and i ... Memftrana limitans externa Outer nuclear layer Outer molecular layer 4. Inner nuclear layer 3. Inner molecular layer 2. Layer of nerve cells 1. Layer of nerve fibers .Membrana limitans interna Inner surface Section of retina. In the center of the retina is an oval spot, the yellotv spot.Here the laj^ers of the retina, except the layer of the rods and HEWES, P. & H, —16 248 PHYSIOLOGY AND HYGIENE cones, are thin, and the cones are, contrary to the conditionelsewhere, thicker than the rods. This is the part of theeye where the image strikes when we look straight at anobject so as to get the clearest vision of it. The blind spot. There is one part of the retina wherethe optic nerve passes through it from the back to the ante-rior surface of the retina, where it spreads out. This spothas no rods and cones, and therefore takes no impressions.It is called the blind spot. This spot can be found by thefollowing experiment: Place upon

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