Pla*cen"ta (?), n.; pl. L. Placentæ (#), E. Placentas (#). [L., a cake, Gr. &?; a flat cake, from &?; flat, fr. &?;, &?;, anything flat and broad.] 1. (Anat.) The vascular appendage which connects the fetus with the parent, and is cast off in parturition with the afterbirth.

&fist; In most mammals the placenta is principally developed from the allantois and chorion, and tufts of vascular villi on its surface penetrate the blood vessels of the parental uterus, and thus establish a nutritive and excretory connection between the blood of the fetus and that of the parent, though the blood itself does not flow from one to the other.

2. (Bot.) The part of a pistil or fruit to which the ovules or seeds are attached.

• (anatomy) A vascular organ in mammals, except monotremes and marsupials, present only in the female during gestation. It supplies food and oxygen from the mother to the foetus, and passes back waste. It is implanted in the wall of the uterus and links to the foetus through the umbilical cord. It is expelled after birth.
  
• (botany) In flowering plants, the part of the ovary where ovules develop; in non-flowering plants where the spores develop.