Butchered animal and left out membranes (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Anagram (butchered) of ANIMA [l], without the L (left). Plural of amnion, the membrane that surrounds an embryo; I didn’t know the word, but I had heard of amniotic fluid so it was straightforward to deduce.