Amniotic membrane (4)
I believe the answer is:
caul
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">amniotic membrane</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for caul that I've seen before include "Membrane covering an infant's head" , "It covers the head at birth" , "Membrane sometimes on head of new-born baby" , "Membrane found on child's head at birth, considered lucky" , "Membrane around fetus" .)