Fundament: an archaic or formal term for the buttocks/anus.

Yer welcome.

Similar etymology to "foundation": both derive ultimately from the same Latin word, "fundo", just from slightly different nominalizations (fundamentum/fundatio). Fittingly enough, that word still means "foundation" in e.g. French, German, and Polish.

fundament is a base of anything, amongst which the buttocks was the fundament of the human anatomy apparently.

A point of view best appreciated from a semi-reclining position.