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7423737 
Journal Article 
Placental Types 
Benirschke, K; Burton, GJ; Baergen, RN; , 
2012 
Springer Berlin Heidelberg 
Berlin, Heidelberg 
Pathology of the Human Placenta 
27-39 
All viviparous vertebrates develop a system of extraembryonic membranes that surround the fetus. The apposition or fusion of these fetal membranes with the uterine mucosa, for purposes of maternal-fetal physiological exchange, initiates the formation of the placenta. The fetus is connected to the membranes by the umbilical cord. The maternal-fetal contact zone, provided by the membranes and the endometrium, represents the placenta.