Evolution

Check Your Face To See Evidence Of A Third Eyelid

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The tiny pink fold of tissue in the corner of your eye is a vestigial remnant! Scientists think that it's all that's left of a nictitating membrane, or third eyelid. Birds, reptiles, amphibians, and fish still have this membrane, which draws across the eye to keep it moist and shield it from debris or water. In humans, it's known as the plica semilunaris, and we can't do much with it except marvel at what it represents: evolution.

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Key Facts In This Video

  1. Whales have vestigial hind-leg bones. 00:07

  2. At a certain stage of development in the womb, all human fetuses have a tail. 01:09

  3. The plica semilunaris in the corner of your eye is the vestigial remnant of a nictitating membrane. 02:05

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