Cells outside the embryo that, although derived from the zygote, are not part of the embryo proper and contribute to the fetal membranes (yolk sac, allantois, amnion, and chorion).
Source: PAC, 2016,
88, 713. (
Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 753 [
Terms] [
Paper]