The umbilical cord connects the baby to the placenta.脐带把婴儿与胎盘连在一起。The drug can be transferred to the baby via the placenta.毒品会通过胎盘传给胎儿。The study sheds light on the genetic differences between placental and marsupial mammals. 这一研究让人了解胎盘哺乳动物和有袋哺乳动物在基因上的差异。