Why so many animals, including our pets, have a third eyelid—yet humans don’t
Our family dog used to have a rather noticeable extra eyelid that became especially apparent when he dozed off, usually upturned on the rug. This is the fleshy curtain seen at the corner of each eye, closest to the nose. It’s also commonly called the nictitating (literally “blinking”) membrane. ⌘ Read more