extraembryonic celom

ex·tra·em·bry·on·ic ce·lom

that portion of the celom external to the embryo; communicates temporarily at the umbilicus with the intraembryonic celom. By the end of the eighth week, growth of the amniotic sac obliterates the celom as the amnion and chorion fuse.
Synonym(s): exocelom, exocoelom

chor·i·on·ic cav·i·ty

(kōr'ē-on'ik cav'i-tē)
The space surrounding the umbilical vesicle (primary yolk sac) and amnionic sac, except where the connecting stalk attaches to the cytotrophoblast of the blastocyst.
Synonym(s): extraembryonic celom.