Fig. 1

Porcine placental barrier and conceptus. Representations of the placental barrier in swine (A) and conceptus within the uterine horn (B). Note that the allantois also supports the vascular elements of the epitheliochorial placenta of the pig. The amnion is filled with amniotic fluid that facilitates the embryo/fetus to allow it to develop symmetrically and not adhere to other tissues