If you think about it, using the outsides of these blood vessels like this is a really clever design solution, because the brain is enclosed in a rigid skull and it's packed full of cells, so there is no extra space inside it for a whole second set of vessels like the lymphatic system.
如果你仔细想想就会发现 利用这些血管外壁 真的是一个巧妙设计的解决方法。 因为大脑在一个坚硬的头骨中 是封闭的， 并且它里面装满了细胞。 所以在大脑中已经没有空余的位置 留给第二套像淋巴系统那样的管路