Hey GatorBoy!! It appears to be the distal part of a Humerus bone on which the proximal Radius and Ulna bone would attach to form the forearm region!! If you turn it upside down it makes more sense and you can visualize what the elbow joint would look like!! By the way thanks for sharing your Electrolysis set up-Pretty Neat!! Anyway, GOOD LUCK and GOOD HUNTING!! VERDE!!