[433] And how does a bhikkhu dwell contemplating the body in the body (kāyānupassī) externally?
Here a bhikkhu reviews the body externally — up from the soles of the feet, down from the tips of the hair, bounded by skin — as full of many kinds of impurity: "There are in his 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, nasal mucus, oil of the joints, and urine."
He cultivates that sign (nimitta), develops it, makes much of it, and determines it well. Having cultivated that sign, developed it, made much of it, and determined it well, he applies the mind (citta) to the body internally and externally.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.