The function Chinese medicine assigns to the Small Intestine is one of its most characteristic pieces of reasoning, and it does not map onto digestion in the modern sense. The organ is described as separating the pure from the impure: receiving what the Stomach has broken down, sending the usable part onward and the rest to the Large Intestine and the Bladder. The same phrase is then used metaphorically, and the classical literature extends the organ's remit to judgement, to the sorting of what should be kept from what should be let go.
That double reading, physical function and mental faculty described in one vocabulary, is not a later mystical overlay. It is how the Inner Canon writes about every organ, and it is one of the clearest structural differences between this system and the biomedical one it is usually compared to. The tradition does not have two languages, one for the body and one for the mind, and it does not treat the distinction between them as fundamental.
The channel runs from the little finger up the back of the arm, across the shoulder blade in a distinctive zigzag, to the ear. It pairs with the Heart as the yang and yin of Fire, and its horary period runs from one to three in the afternoon.
The atlas reports the tradition's own account. It does not claim that the small intestine performs any of the functions described here, and none of this is medical guidance.