Shank is a great cut for soup and there is a nice clump of marrow in every bone. I was selling shank soup bones and meatless bones real cheap at the grocery store so the people who could not pay big bucks for grass fed beef could at least make soup. Those bones sold as fast as I could put them out. They cook down the knuckle bones for collagen or something and, like you said, marrow is some of the richest food around. A lot of people in cancer recovery were requesting the shank bones--for the marrow?