《黄帝内经·素问·太阴阳明论》
所以说： 阳经的病邪，先上行至头顶再向下行；阴经的病邪，先下行至指端，再向上行。 
故曰： 阳病者上行极而下，阴病者下行极而上。 
Therefore, it is said that: the pathogenic factors of the Yang meridians first ascend to the top of the head and then descend; the pathogenic factors of the Yin meridians first descend to the fingertips and then ascend.