Which preposition to use with fundaments

after Occurrences 2%

It is also obligatory upon them to go to stool every morning; to use the left hand only in wiping themselves; to wash their fundaments after stool; to wash their whole persons and clothing every day; and, finally, also to rinse their mouths with water, and this they often do after washing in foul tanks, or still fouler pools of water.

of Occurrences 1%

The Muhammedans were thus obliged to accept Christian hypotheses on theological points and the fundaments of Christian and Muhammedan culture thus become identical.

Which preposition to use with  fundaments