Soon the caudal, or lower, end of the tube stretches out, forming the spinal cord, while the cranial end begins to expand, divide, and enlarge into three primary brain vesicles, or interconnected chambers.

很快，管子的尾端或下端伸出，形成脊髓，而颅端开始扩张、分裂和扩大成三个主要的脑囊泡，或相互连接的腔室。