File:The human body and health - an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools (1908) (14586335080).jpg

Identifier: humanbodyhealthe00davi (find matches)
Title: The human body and health : an elementary text-book of essential anatomy, applied physiology and practical hygiene for schools
Year: 1908 (1900s)
Authors: Davison, Alvin, 1868-1915
Subjects: Physiology Hygiene
Publisher: New York : American Book Company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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THE WALLS Oil COATS OF THE EYEBALL 247 and the upper and lower muscles turn the ball upwardand downward respectively. Two oblique muscles giveother motions to the ball. Cross eyes are caused by theinner recti muscles being stronger than the outer ones. The Parts of the Eye. — The complete eye consists ofthe eyebrows, whichprevent the perspira-tion from r u n n i n gdown into the eyeball,the eyelids, whichprotect the eyeballin front, and the eye-ball itself. The eyeballis nearly spherical,and consists of anouter wall one tenthof an inch thick filledwith three transparentsubstances, called hu-mors. As the eye of Fig. 159a cow, pig, or cat has
Text Appearing After Image:
Horizontal section through the eye. a, aqueous humor; ac, fovea; h, blind spot; ci, fibers of ciliary muscle; co, the same structure as cornea; ch, choroid coat; z>, iris; Z, crys- a human eye, the dis- ^allinelens: n, ciliary processes: op, optic •^ nerve; s, sclerotic coat. section or cutting apart of the eyeball of any one of these animals will be a great help to pupils in their study of the organ of sight. The Walls or Coats of the Eyeball.—The wall of theeyeball is composed of three coats. The outer coat consistsof the tough and thick sclerotic part behind, and the trans-parent cornea in front. The midclle coat^ about as thick aspaper, is formed largely of the black choroid portion, con- 248 THE SE>s^SE OKGANS tinuous ill front with the iris appearing blue, gray, orbrown according to the color of the eye. A circularopening in the center of the iris is the pupil^ throughwhich light passes to the interior (Fig. 159). By meansof muscular libers forming part of the iris the

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