So, what was a third eyelid doing in a human? Most refer to such bits of tissue as vestigial. The word means a structure that ...

and the tear gland in that third eyelid can become blocked in dogs (and rarely in cats). This gland will then swell and pop out in front of their eyeball, leading to a red, cherry-like swelling ...

According to IFLScience, the third eyelid protects the eye from debris and helps spread tears, which is particularly ...

However, her third eyelid flap – a structure that supports a weakened cornea and protects the eye surface – remained visible. The veterinary team confirmed that the injury would not affect her ...