Here's a quote from the Dhatu-vibhanga Sutta (MN 140):
I see section 14 on the elements is missing from Access To Insight's Samyutta Nikaya. I'm wondering if it would be worth spending $60 just to see that section, and the other texts. Or if it would be better to just get Stephen Snyder's $13 book. Mmm..."And what is the earth property? The earth property can be either internal or external. What is the internal earth property? Anything internal, within oneself, that's hard, solid, & sustained [by craving]: head hairs, body hairs, nails, teeth, skin, flesh, tendons, bones, bone marrow, kidneys, heart, liver, membranes, spleen, lungs, large intestines, small intestines, contents of the stomach, feces, or anything else internal, within oneself, that's hard, solid, and sustained: This is called the internal earth property. Now both the internal earth property & the external earth property are simply earth property. And that should be seen as it actually is present with right discernment: 'This is not mine, this is not me, this is not my self.' When one sees it thus as it actually is present with right discernment, one becomes disenchanted with the earth property and makes the earth property fade from the mind.