N → another name for nictitating membrane
You may not know it, but you have a third eyelid.
你可能不知道第三眼睑,但你拥有它。
Humans have a remnant (but non-working) third eyelid (you can see it in the picture above).
人类还保留着第三眼睑的痕迹(没有用,图片中可以看到)。
Eyes should be clear and bright. No discharge and no sign of the third eyelid.
眼睛应是清洁明亮的,没有污垢及外露的第三眼睑。
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