In fact, the first meaning of the word ass is a donkey. Which has ears. Moreover, in Jerome's time it was the only meaning in the written language; the meaning of "Jop" appeared much later. So the translation is correct.

I will add, the British "ass" (asshole) rebirthed into the American "ass" (jopa) through the idiom "asshole". In the original - "the donkey hole", which subsequently changed the smiles to simply "the donkey", because Americans like to shorten words to one, usually the first slang. Thus, the English "seat" turned into the American "jopa". But we laugh at them not just because of that :)