The same way cells that form the limb become more like muscle cells or skin cells, or the structures that become the limb.

同样的,形成上肢的细胞,变得越来越像肌肉或皮肤细胞,或者上肢的其他结构

耶鲁公开课 - 生物医学工程探索课程节选

You can see this region here is going to develop into one of the upper limbs, the arms here and the back is different from the front, the spinal cord is developing in the back, whereas, the structures that become our intestinal tract is developing on the other surface.

你能看到这个区域,将会发育成为上肢,这里是手臂,而且身体前后也有不同,脊椎正在后背发育,另外,会成为我们肠管的结构,也在另一个表面发育着

耶鲁公开课 - 生物医学工程探索课程节选