Essay seed — from the Nyasa Yoga ingest. Not drafted; this is the argument and the spine. [WILDCARD]
Try to teach somebody, in the year 900, to put their attention on their own kidney.
You can't show them a kidney. Nobody has drawn one accurately, and if they had, no two copies would agree. All you can do is point at your own back and say around here.
So you invent a picture. A lotus, with a fixed number of petals, a colour, an animal, a syllable. Something a person can hold in their head and come back to tomorrow.
Twelve centuries later the pictures are still in every yoga studio in the world, and the thing they were substituting for is available on a phone in four seconds.
1. The diagram was a workaround for a missing technology. That's the claim, and it's checkable in an unexpected way. The root chakra is drawn as a square — and the perineal muscles, seen from below, form a square: two muscles at the corners, one running as the diagonal, one bent to close it. The sacral chakra is a triangle, and the sacrum is triangular. Somebody looked, or somebody felt, and drew what they found in the only notation available. See The Diagram Stood In for an Anatomy Book.
2. The petal counts came off a spine. Six at the sacrum, because six nerve sets leave it. Ten at the navel, from five lumbar pairs. Twelve at the heart, sixteen at the throat. Four of the traditional numbers land against an anatomy chart without adjustment. See The Petals Are Spinal Nerve Roots.
3. Then the puzzle nobody could explain. Moses has two horns of wisdom. Yamāntaka has two horns. Isis holds a sun between two horns. The wish-giving cow has two. It recurs across traditions with no contact and it's always attached to attainment — and on a diffusion tensor scan the spinal cord splits upward into two ascending branches, one into each hemisphere, reaching higher than anything else. The tantric instruction that goes with the image is to visualise a sun above your head, so that attention travels up both.
4. And the same reading turns up somewhere with no possible connection. A goddess on an Egyptian relief carries a bilobed object with two horns on her head. Egyptologists identify it and are vague about the meaning. The reading from inside a different living tradition: it's a location marker, telling you which region of the body she's in. Two practitioners, two continents, one method — the thing on the head is a pin dropped on a map. See What She Wears Is Where She Is.
A notation built to compensate for a missing instrument will outlive the instrument's arrival, and will be read as doctrine by everybody who never knew what it was standing in for. Which makes obsolete notation one of the more reliable places to go looking for what a tradition actually knew — because the thing it encoded is still in there, and the encoding survived precisely by being mistaken for something else.