after posting the last post, it reappeared, so I watched it to it's end.
That bone is called the AITCH bone (pronounced "H"), one of three major bones in the leg. It is connected to the FEMUR bone, the long bone in the ham, which is then connected at the other end to the HOCK of the leg bone in the shank. you can also remove the hock too, just leaving the femur bone inside, or remove the femur also, cutting into the leg to do so, but also opening the leg so it is no more than 2" thick at any point, eliminating the chance of 'bone sour', or getting cure or salt to the meat before it spoils, or sours. This is a pic of the bone structure on a leg I did: