英语语法分析

Extraembryonic mesoderm migrates through primitive streak to the presumptive yolk sac between days 6.5 and 7.0 of gestation.

胚外中胚层在妊娠的第6.5至7.0天之间通过原始条带迁移到推测的卵黄囊。

In the center layer (mesoderm) the heart and circulatory system are forming.

在中胚层，心脏和循环系统正在形成。

In the center layer (mesoderm), the heart and circulatory system are forming.

在中胚层，心脏和循环系统正在形成。