Fundament

"Where's Tom?" "Up his own fundament."

It [the Sphincter Ani] serves to purse up the Fundament, and so hinders the involuntary Evacuation of the Fæces.

ANOTHER defect that new-born infants are liable to is, to have their fundaments closed up; by which they can never evacuate the new excrements engendered by the milk they suck […]

Bathe the parts frequently with cold water, and, if there be much pain at stool, always squirt up the fundament, beforehand, with a syringe, half a teacupful of cold water.

I flinched when he touched my rosebud, but pretty soon I was fucking his mouth like it was Hector's fundament.