状体板 耳板 板一 额鼻隆起 上頜隆起一 个下饿隆起 i 原始咽 心隆起 心壁 by the 4th week, frontonasal prominence mesenchymal proliferation of ventral surface of brain vesicle --heart prominence: development of heart---by the 4 th week, ---frontonasal prominence: mesenchymal proliferation of ventral surface of brain vesicle ---heart prominence: development of heart