Osteomancy is divination by bone, and the single name covers two quite distinct procedures often conflated. In the first, a bone is heated until it cracks, and the resulting network of cracks is read. This is the celebrated method of the Chinese oracle bones of the Shang dynasty (roughly the second millennium BCE): diviners applied heat to the shoulder-blades of oxen and the plastrons of turtles, interpreted the cracks that formed as the gods' or ancestors' answer to a posed question, and then, crucially for history, inscribed the question and often the outcome beside the cracks. These inscriptions constitute the earliest substantial body of Chinese writing yet known, and they are a primary source for the religion, kingship, and language of the Shang, making this form of osteomancy one of the most historically consequential divinatory practices in the world. (The related practice of reading the cracks in heat-treated turtle shells is sometimes distinguished as plastromancy.)
In the second, quite different procedure, the form of a bone is read, most familiarly the wishbone or, in the practice known as scapulimancy in its non-heated form and in many pastoral cultures, the natural markings and shape of an animal's shoulder-blade after it is cleaned. Osteomancy thus reflects a widespread intuition that the bodies of sacrificed or slaughtered animals, and especially their bones, carry legible signs of the divine will.