BT Ḥul 52a(32) :הת׳ בוכנא בלא אסיתא הכא בוכנא ו̇א̇סיתא‏ : there we are dealing with the pestle (i.e. rib) without the socket, here the pestle and the socket [in a discussion of broken ribs and their connection to the spinal column]
See the entire entry for būḵān, būḵānā n.m. pestle