Mouse-human differences: The mouse and human placentas have labyrinthine and villous types of interdigitation between maternal and fetal tissues, respectively ... The mouse placental labyrinth is composed of an intricate network of maternal blood spaces and embryonal blood vessels. Maternal and embryonal blood is separated by a placental barrier that consists of four cellular layers: layer I trophoblasts line the maternal lacunae, trophoblasts in layers II and III form syncytial-like layers, and endothelial cells line the embryonic vessels[DOI: 10.1073/pnas.96.14.8138 ]

The placental layers where embryonic blood vessels are surrounded by trophoblast cells and maternal blood

placental labyrinth

labyrinthine layer

labyrinthine layer of placenta

uberon

UBERON:0003946

http://purl.obolibrary.org/obo/NCBITaxon_9606

http://placentation.ucsd.edu/placenta.html