<taps head> bone structure is probably the definitive here ... if it's a 1/2 butt there will be a single bone, on a whole butt this bone is sort of the shape of 'trinity' if that makes sense. Anyway, there would be a single half of one of these bones. If it's a picnic lower half there will be a single tube shpaed bone, if it's a picnic upper half there would be a portion of the tube shaped bone connected to a joint ... a mass of cartiledge.