Gross structure of the agouti placenta. (A) Transverse section of the placenta in midpregnancy showing the labyrinth (lab) of the main placenta and the subplacenta (sub pl). Fetal vessels run from the umbilical cord to the subplacenta through the central excavation (arrow). Scale bar: 1 cm. (B) Placenta injected with Neoprene latex to show the vascularization of the subplacenta. Fetal arteries are in white, while maternal arteries in the decidua (arrow) are in red; maternal venous channels were filled with green latex. (C) Schematic to show location of the subplacenta in relation to the yolk sac placenta, main placenta and decidua. The labyrinth occurs in lobes separated by interlobar trophoblast. In addition to the decidua beneath the subplacenta, maternal tissue forms a capsule that houses the placenta. The trajectory of the fetal vessels is also indicated (arrow).