birds' eyes
... that birds' eyes have three lids, including the nictitating membrane , which moves across the eyeball horizontally?
... that <b id="mwC-A"><a href="./Bird_vision" id="mwC-E" rel="mw:WikiLink" title="Bird vision">birds' eyes</a></b> have three <a href="./Eyelid" id="mwC-I" rel="mw:WikiLink" title="Eyelid">lids</a>, including the <a href="./Nictitating_membrane" id="mwC-M" rel="mw:WikiLink" title="Nictitating membrane">nictitating membrane</a> <i id="mwC-Q">(pictured)</i>, which moves across the eyeball horizontally?