Placenta developed from the allantois and chorion, establishing a nutritive and excretory connection between the blood of the fetus and that of the mother.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 735 (https://doi.org/10.1515/pac-2015-1202)