#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

No statement uses or specializes nictitating_membrane; click here to add one.