part of part of in taxon develops from develops from composed primarily of spongiotrophoblast cell Rodentia cell layer placenta spongiotrophoblast layer restriction to Rodentia may be too strong - we apply it for now as we are inheriting the MP definition spongiotrophoblast layer of placenta BTO:0005402 EMAPA:31876 UBERON:0004021 The structure of the outer structural layer of the rodent placenta[MP]. Forms a compact layer of non-syncytial cells between the labyrinth and the outer giant cells spongiotrophoblast In the absence of direct lineage analysis, it has been assumed, from histological studies and from the continuity of marker gene expression, that the spongiotrophoblast largely derives from the cells of the ectoplacental cone ectoplacental cone reproductive structure extraembryonic tissue