third eyelid

1. Ocular tumors in dogs are found in the eyelid, conjunctiva, third eyelid, cornea, sclera, iris, ciliary body, retina, choroid, optic nerve, and orbit.
   犬类的眼部肿瘤发现于眼睑，结膜，第三眼睑，角膜，巩膜，虹膜，睫状体，视网膜，脉络膜，视神经和眼眶。
2. Signs include enophthalmos ( sunken eye), miosis ( small pupil), elevated third eyelid, and ptosis ( drooping of the upper eyelid).
   第三眼睑上移和上眼睑下垂。

noun

1. a protective fold of skin in the eyes of reptiles and birds and some mammals

   Synonym:    nictitating membrane