[Anatomical basis of transition from eleven to twelve meridians in Han dynasty]

The discovery of modern evolutionary anatomy shows that the persistent median artery in the upper arm is a common variant with an increasing trend. This phenomenon can explain well the transition from the eleven meridians described in the Han silk and bamboo slips to the twelve meridians finalized in Neijing and the addition of the hand- jueyin meridian in Han dynasty. After systematic analysis and comparison, the author proposes the hypothesis that "yin meridians are arteries, and yang meridians are nerve-like structures" to explain the meridian theory prior to acupuncture and acupoints in the Qin and Han dynasties. It is clear that over two thousand years ago, Chinese physicians already described the distribution, physiology, and pathology of the six main arteries and six important nerves in the human extremities. The finding suggests that it was the addition of acupuncture and acupoints that had changed the direction of TCM development in Neijing or later and promoted the maturation of qi and blood, meridians, and zangfu theories.