allantois (n.), allantoic (adj.)

https://doi.org/10.1351/goldbook.10356

Extra-embryonic membrane formed early in development as an outpouching of the yolk sac into the area of the future umbilical cord.

Note: Blood vessels of the allantois become the umbilical artery and umbilical veins.

Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 719 (https://doi.org/10.1515/pac-2015-1202)