Outlines of human physiology; designed for the use of the higher classes in common schools . , and others again are of opinion, that it isformed in part from one of the coverings of the eye,and that it has also a layer peculiar to itself. Theback part of the iris is called the uvea. The iris di-vides the space between the crystalline lens and thefront of the eye into two parts, called the anterior and SENSE OF SIGHT. 183 posterior chambers, the former of which is much largerthan the latter. All the light admitted to the eye,passes through the opening in the iris, and it is suppliedwidi muscula
Outlines of human physiology; designed for the use of the higher classes in common schools . , and others again are of opinion, that it isformed in part from one of the coverings of the eye,and that it has also a layer peculiar to itself. Theback part of the iris is called the uvea. The iris di-vides the space between the crystalline lens and thefront of the eye into two parts, called the anterior and SENSE OF SIGHT. 183 posterior chambers, the former of which is much largerthan the latter. All the light admitted to the eye,passes through the opening in the iris, and it is suppliedwidi muscular fibres, by which this opening can be di-lated and contracted. The eye has three coats or coverings. The outer,which is called the sclerotic, is a firm, fibrous mem-brane, w4iich serves to defend the eye from injury, andinto which the muscles, that move it in various direc-tions, are inserted. It extends over the whole of theeye, except the fore part, where a transparent mem-brane, called the cornea, is situated. It is the scle-rotic coat that is known by the name of the white othe A Sectiok of the HomaK Eye. a The aqueous humor, h The crystal-line l-^ns. c The vitreous humor, d is an object from which the rays otlight go off, and as tliey enter the eye, they are refracted by the diflferenthumors, and form an inverted image, e, on the retina. Within the sclerotic coat is situated the choroid is a thin, delicate membrane, composed in greatmeasure of blood-vessels and nerves. It is loosely at-tached to the sclerotic coat, which it covers, and is ofthe same form and extent. On the surface of the cho-roid coat is found a dark substance, called the black 184 SENSE OF SIGHT. pigment, which is of great importance in the functionof vision. The inner coat of the eye, if it be not an expansionof the optic nerve, is composed of nervous filaments,and is called the retina. It is of the same extent as theother coats, surrounding the whole globe of the eye,except the circular o
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