Tucked away mostly unnoticed into the corner of your eye is small fold of membrane that serves practically no purpose whatsoever.

Plica semilunaris. 11. All humans have a plica semilunaris, also known as a third eyelid or nictitating membrane. But this tiny fold of tissue next to the tear duct in the corner of your eye is ...

Just next to it is a thin strip called the plica semilunaris, and it may surprise you to learn that it’s a third eyelid. Or, perhaps we should say, it’s the evolutionary leftovers of the ...

This, along with the Plica semilunaris, which is that little membrane just next to it, are actually thought to be the vestigial leftovers from your "third eyelid".

You’ll notice a small patch of pink called the plica semilunaris. This is the remnant of a nictitating membrane, which likely first protected your ancestors eyes as they were hunting down prey ...

The Plica semilunaris is the red, fleshy-looking structure in the corner of your eye. This used to be a second eyelid. This eyelid was transparent, so it could blink and the animal could still see ...

This is called the plica semilunaris, or the nictitating membrane. Birds and reptiles have these extra translucent eyelids which they can put across their eyes for protection or moisture while ...

But there is a weirder one, the plica semilunaris. The next time you look into the eyes of a loved one (it’s more awkward with a stranger on the bus), look at that little pink, triangular bit on ...

The caruncle is a small mound of medial canthus tissue containing fine hairs, sebaceous glands and sweat glands. The plica semilunaris is a vertical fold of skin lateral to the caruncle.

If you have plica syndrome, your knee may hurt and swell. It may lock, give way, catch, or make a clicking sound. People with the condition say their knee doesn’t feel stable.