BSIP CHNO LIOTET / SCIENCE PHOTO LIBRARY BSIP CHNO LIOTET / SCIENCE PHOTO LIBRARY
Iris. Coloured scanning electron micrograph (SEM) of part of the iris in the eye. The iris is a muscular disc which surrounds the pupil. The pupil margin is out of shot at the bottom of the frame. The radial lines (running from bottom to top) are layers of smooth muscle which contract to open the pupil wider. The horizontal lines (left to right banding) are layers of muscle which contract to shrink the pupil. The pupil is thus kept at the optimum aperture for the light conditions. Magnification unknown.
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