#nictitating_membrane__nictitatingmembrane__thirdeyelid  a protective fold of skin in the eyes of reptiles and birds and some mammals
  supertype:  #protective_fold  a flap of tissue that protects what it covers
  subtype:  #haw  the nictitating membrane of a horse
  part of:  #eye__oculu__optic__peeper  the organ of sight (`peeper' is an informal term for `eye')
     part of:  #visual_system  the sensory system for vision
     part of:  #human_face__humanface  the front of the head from the forehead to the chin and ear to ear; "he washed his face"; "I wish I had seen the look on his face when he got the news"
        part of:  #head__caput  the upper or front part of the body in animals; contains the face and brains; "he stuck his head out the window"
           part of:  #animal__animate_being__animatebeing__beast__brute__creature__fauna  a living organism characterized by voluntary movement

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