Source : Webster's Revised Unabridged Dictionary (1913)

Placentation \Plac`en*ta"tion\, n.
   1. (Anat.) The mode of formation of the placenta in different
      animals; as, the placentation of mammals.

   2. (Bot.) The mode in which the placenta is arranged or
      composed; as, axile placentation; parietal placentation.

Source : WordNet®

placentation
     n 1: the formation of the placenta in the uterus
     2: arrangement of the ovules in the placenta and of the
        placentas in the ovary