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To preserve the transparency of the cornea, and also to lubricate the eyelids and aid in the removal of foreign bodies, a secretion, called tears, is constantly supplied. The lachrymal, or tear, glands are situated at the upper and outer margins of the orbits. They have the general structure of the salivary glands and discharge their liquid by small ducts beneath the upper lids.
They were beautiful eyes, and charged with something more than their own beauty. With a deep brunette setting even to the darkened cornea, the pupils were blue as the sky above them. But they were lit with another intelligence. The soul of the Salem whaler looked out of the passion-darkened orbits of the mother, and was resistless.
In certain star-fishes, small depressions in the layer of pigment which surrounds the nerve are filled, as described by the author just quoted, with transparent gelatinous matter, projecting with a convex surface, like the cornea in the higher animals. He suggests that this serves not to form an image, but only to concentrate the luminous rays and render their perception more easy.
It is known as interstitial keratitis, and takes the form of a gradual, slow clouding of the clear, transparent convex surface of the eyeball, the cornea, through which the light passes to reach the lens. While the process is active, the child is made miserable by an extreme sensitiveness to light, the eye is reddened, and there is pain and a burning sensation.
For in these latter the cornea is at first perforated, while different degrees of perforation of the same part are presented by different adult cuttle-fishes large in the calamaries, smaller in the octopods, and reduced to a minute foramen in the true cuttle-fish sepia.
It is pierced at the back by a small opening which admits the optic nerve, and in front it becomes changed into the peculiar tissue that makes up the cornea. The cornea forms the transparent covering over the lesser spherical segment of the eyeball, shading into the sclerotic coat at its edges. It has a complex structure, consisting in the main of a transparent form of connective tissue.
Besides these three coats, and the cornea which constitutes about one fifth of the anterior portion of the outer coat, it is necessary to notice the iris, so called from its variety of color in different persons, and upon which alone the color of the eye depends. The iris is a circular membrane situated just behind the cornea, and is attached to one of the coats at its circumference.
Michael gazed at her as a son would gaze at his mother, when it is for the last time. The tears, which his pride in vain endeavored to subdue, welling up from his heart, gathered under his eyelids, and volatiliz-ing on the cornea, had saved his sight. The vapor formed by his tears interposing between the glowing saber and his eyeballs, had been sufficient to annihilate the action of the heat.
For this purpose the point of an Edison electric pen is armed with a small ivory ball, and the vibration rate varies from 200 to several thousand a minute, the rapidly revolving ball being passed over the closed lids, in some instances directly upon the cornea itself.
To this coat, which serves as a kind of framework for the eye, are attached the muscles which move the eyeball. In front of the globe, the sclerotic passes into a transparent circular portion forming a window through which one can see into the interior. This is the cornea.
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