BT Qid 71b(6) :מטו ^ל^ערקמא דמיא ארכביה לר׳ יוח׳ אכתפיה וקא מעבר ליה‏ : when they came to a pool of water he mounted PN on his shoulders and was taking him across
See the entire entry for ˁrqwm n.m. bend of an animal's hind leg