I’d like to try to describe what I see in the lines of the illustration from “The Secret of the Golden Flower” (a Chinese meditation manual now dated somewhere between 1668 and 1692):
The lines up the leg parallel the ilio-tibial tract, a fascial band which stretches from the lower leg to the pelvis, and to which the tensor and gluteous muscles attach.
The tensor and gluteous muscles are a part of two focuses for stretch and resile in the fascia of the lower body, one lying just below the navel and the other just behind the sacrum and lower spine.
From behind the sacrum, stretch and resile can align and guide the displacement of the fascial sheet behind the lower spine:
Support provided by the displacement of the lower back fascia allows for an alignment of the spine that fosters ease in the nerve exits between vertebrae. Ease in the nerve exits between specific vertebrae corresponds with an ability to feel at the surface of the skin in particular areas:
(Thibodeau Patton, 1999)
In my experience, the ability to feel to the crown of the head and into the lower abdomen (as pictured in the “Golden Flower” illustration) is actually a function of the relinquishment of activity, particularly with regard to the movement of breath. Rujing advised that inhalation “enters and reaches the tanden, and yet there is no place from which it comes… breath emerges from the tanden, and yet there is nowhere it goes”. For me, the two-part “enters and reaches” describes an autonomic coordination of the displacements behind the sacrum and lower back in inhalation, given sufficient feeling throughout the body; feeling throughout the body, in turn, depends on the inclusion of all the senses, and even what lies outside the range of the senses, in the relinquishment of activity in the movement of breath.