Ultrastructure of the labyrinth in mid gestation. (A) Necromys (MZUSP/APC 1246-3). The placental barrier separated a maternal blood channel (MBC) and a fetal capillary (FC) with intact endothelium (EC) and a red blood cell (RBC). (B) Necromys (MZUSP/APC 1246-3). The placenta comprised three trophoblastic layers (TI, TII and TIII). (C) Euryoryzomys (MAV/SJB 02). The hemotrichorial placenta. (D) Necromys (MZUSP/APC 1246-3). There was a strong contact between layer TIII and the basement membrane of the endothelial cell (arrow). Different types of junctions occurred between trophoblast layers TII and TIII, including tight junctions (TJ), intermediate junctions (CJ) and desmosomes (circle). (E) Necromys (MZUSP/APC 1246-3). The outermost layers in detail. (F) Euryoryzomys (MAV/SJB 02). Two cells belonging to layer TI.