Fig. 1

Gross morphology and microvascular architecture of the hystricomorph subplacenta. A^I – A^III Capybara (Hydrochaeris hydrochaeris) around 90–140 days of gestation. A^I Sagittal section through the placenta showing the relationship among the chorioallantoic placenta (P), the subplacenta (Sp) and the basal deciduous (Bd) and the mesometrial side (Mes); A^II Schematic drawing illustrating the relationship between the fetus (F), umbilical cord (Uc), yolk sac (Ys), Sp and Bd, and anti-mesometrial (Ant) of the uterus; A^III Corrosion model of the capybara which the different types of microvascularization of the placental lobes (PL) and Sp are observed. Placental vessels were injected with methacrylate and subjected to the corroding process. The relationship between Sp microvessels and larger vessels is verified (arrow), which possibly carry products produced by the subplacenta during this gestation phase - PP (placental peduncle) FU (umbilical funiculum). B Rock cavy (Kerodon rupestris) around 76 days: Placenta injected with methacrylate submitted to corrosion showing the central vessels (CV) and peripheral vessels (PV) in relation to the chorioallantoic placenta (P) and Sp. C Paca (Agouti paca) around 45–70 days: In C, the paca placenta injected with latex, the maternal vein injected with green, maternal artery with white, fetal vein with yellow and fetal artery with red. Note, the Sp appeared to have regressed in size at term compared with mid-gestation. D^I – D^II Agouti (Dasyprocta leporine) around 35–50 days: In D^I, model of microvascularization of the agouti subplacenta, showing the central vessels injected in blue latex and the subplacenta in white latex. D^II Showing the P and Sp and also the umbilical cord (Uc)