The ____ surface of the central portion of the allantois fuses to the _____ surface of the amnion to form an allantoamnion. The rest of the allantois fuses with the ____ (except the necrotic tips) to form _____. The allantoamnion and allantochorion are both vascularized by the _____ circulation; the latter forms part of the Pars fetalis of the placenta. Hippomanes are occasionally found in the allantoic fluid.