part of part of has part has part extraembryonic structure decidua chorionic villus placental cotyledon https://upload.wikimedia.org/wikipedia/commons/3/30/Placental_cotyledon.png Rodents have a single cotyledon (called a discoid placenta), whereas humans have multiple cotyledons, although they are consolidated into a cluster that resembles a single disc[PMID:19829370] UBERON:0010008 discoid placenta placenta cotyledon SCTID:256491001 NCIT:C34135 Round structure consisting of chorionic villi[PMID]. A separation of the decidua basalis of the placenta, separated by placental septa. Each cotyledon consists of a main stem of a chorionic villus as well as its branches and subbranches. The cotyledons receive fetal blood from chorionic vessels, which branch off cotyledon vessels into the cotyledons, which, in turn, branch into capillaries. The cotyledons are surrounded by maternal blood, which can exchange oxygen and nutrients with the fetal blood in the capillaries[WP]. Wikipedia:Placental_cotyledon in ruminants, this is cotyledon UMLS:C0242769