BT Ḥul 76a(22) :דעילוי דערקומא, יתיב ההוא מרבנן קמיה דר׳ אבא ויתיב וקאמ׳, דערקומ{{ה}}^א^ גופא‏ : "those sinews) above the bend", one of the rabbis sat before PN, sat and was saying, "the bend itself"
See the entire entry for ˁrqwm n.m. bend of an animal's hind leg