Figure 2.

Schematic view of the fetal membranes and the placenta. (A) The schematic view demonstrates the arrangement of the mesometrially situated embryo, the chorioallantoic placenta, positioned at the antimesometrial side, and the other fetal membranes inside the uterus, representing an advanced stage of pregnancy. (B) In initial pregnancy, the placenta contains mainly of trophospongium with the developing subplacenta confluent to the main placenta. Strings of extraplacental trophoblast and syncytial streamers can be followed from towards the maternal blood channels. (C) In early pregnancy, a labyrinth is established and the subplacenta represents a distinct organ. (D) Near term, the placenta is highly villous with the labyrinth as the dominant area. The subplacenta has been reduced. Red numbers in white boxes refer to subsequent figures with more detailed documentation of specific regions. Ce = central excavation, lab = labyrinth, mbc = maternal blood channel, pys = parietal yolk sac, sp = subplacenta, sys = syncytial streamers, tsp = trophospongium, uc = umbilical cord, ut = uterine tissue, vys = visceral yolk sac.