Hunter gatherers prized bone marrow for its high calorie content; in the modern world, its more like a form of gluttony.
Marrow has slowly crept towards the territory of latest gastronomic fad appearing on an increasing number of menus. While all bones have marrow, the best for eating tend to be large and thick; even these have little substance to them.
The bone is split and cooked leaving a gelatinas substance that can be eaten with a spoon or spread across toast. Calorie rich, its like eating butter.