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要说肚脐是怎么形成的，就要先说说脐带。我们都知道每个胎儿都要在母体中孕育十个月左右才会来到这个世界。在这段漫长的时间里，胎儿是如何隔着羊水、羊膜、子宫、腹腔的层层阻隔，获得氧气和营养物质的呢？
原来，在受精卵着床于子宫内膜之后，胚胎的部分胚膜和相
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