The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil. In humans the pupil is round, but other species, such as some cats, have vertical slit pupils, goats have horizontally oriented pupils, and some catfish have annular types. In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. The image of the pupil as seen from outside the eye is the entrance pupil, which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil.
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Famous quotes containing the word pupil:
“Parental attitudes have greater correlation with pupil achievement than material home circumstances or variations in school and classroom organization, instructional materials, and particular teaching practices.”
—Children and Their Primary Schools, vol. 1, ch. 3, Central Advisory Council for Education, London (1967)
“Yet, if the pupil be of a texture to bear it, the best university that can be recommended to a man of ideas is the gauntlet of the mobs.”
—Ralph Waldo Emerson (1803–1882)
“It belongs to the humanity of a master to warn his pupil about himself.”
—Friedrich Nietzsche (1844–1900)