[432] And how does a bhikkhu dwell contemplating the body in the body (kāyānupassī) internally?
Here a bhikkhu reviews the body internally — up from the soles of the feet, down from the tips of the head-hair, bounded by skin — as full of many kinds of impurity: "There are in this body head hairs, body hairs, nails, teeth, skin, flesh, sinews, bones, bone marrow, kidneys, heart, liver, pleura, spleen, lungs, intestines, mesentery, contents of the stomach, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, snot, synovial fluid, urine."
He pursues that sign (nimitta), develops it, makes much of it, and defines it well. Having pursued that sign, developed it, made much of it, and defined it well, he directs the mind (citta) to the body externally.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.