And further, monks, a monk reflects on this very body enveloped by the skin and full of manifold impurity, from the soles up, and from the top of the head-hairs down, thinking thus: "There are in this body hair of the head, hair of the body, nails, teeth, skin, flesh, sinews, bones, marrow, kidney, heart, liver, midriff, spleen, lungs, intestines, mesentery, gorge, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovial fluid, urine." ... Just so, monks, a monk reflects on this very body enveloped by the skin and full of manifold impurity, from the soles up, and from the top of the head-hairs down, thinking thus: "There are in this body hair of the head, hair of the body, nails, teeth, skin, flesh, sinews, bones, marrow, kidney, heart, liver, midriff, spleen, lungs, intestines, mesentery, gorge, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovial fluid, urine."
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And further, monks, as if a monk sees a body dead one, two, or three days; swollen, blue and festering, thrown in the charnel ground, he then applies this perception to his own body thus: "Verily, also my own body is of the same nature; such it will become and will not escape it." ... And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to a skeleton with some flesh and blood attached to it, held together by the tendons ... And further, monks, as if a monk sees a body thrown in the charnel ground and reduced to a skeleton blood-besmeared and without flesh, held together by the tendons... his mindfulness is established with the thought: "The body exists," to the extent necessary just for knowledge and mindfulness, and he lives detached, and clings to nothing in the world.
http://www.accesstoinsight.org/lib/a.../wheel019.html