| Amnion (n.) A thin membrane surrounding the embryos of mammals, birds, and reptiles. Thesaurus Entries allantoic membrane, amniotic sac, arachnoid membrane, basement membrane, conjuctiva, eardrum, hymen, maidenhead, membrana serosa, membrana tympana, membrane, meninges, meninx, neurilemma, pellicle, pericardium, perineurium, pleura, serosa, tympanic membrane, tympanum, velum |