Saddle : nf (word from latin saddle, circa 1460 sele "comfortable chair").
To have a bowel movement: to defecate.
By extension (late XNUMXth century): Stools: faeces.
Going to the saddle: This expression dates from the XNUMXth century. the word saddle comes from the XNUMXth century, from the Latin sella, which designated a seat, and more precisely the seat of craftsmen who worked seated or the seat of teachers, but also the seat of riders or, in other words, the saddle of a horse.
When the word appears in French, it is also used to name a pierced chair which will be called successively easy saddle, saddle needed and pierced saddle. It is from this chair, the ancestor of our toilet bowl that at the end of the XNUMXth century, by metonymy, saddle (in the singular) designates excrement. And it is from there, that a little later is born the expression bowel movement ( defecate).