metadiscoidal

from The Century Dictionary.

• In embryology, noting the placenta of certain mammals such as the primates (man and apes), in which the villi are restricted to a disk-shaped chorionic area on the ventral side of the embryo.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Anat.) Discoidal by derivation; -- applied especially to the placenta of man and apes, because it is supposed to have been derived from a diffused placenta.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective anatomy Discoidal by derivation; applied especially to the placenta of humans and apes, supposed to have been derived from a diffused placenta.