Definition: Calathisci is a term used in the Greek and Roman mythology to refer to the large, spherical bones that are found in the head of certain animals. These bones are often referred to as "calathes" because they are thought to have been created by the god Poseidon. The specific type and size of these calathes can vary greatly among different animal species, but they are generally considered to be large, spherical structures with a high density of calcium carbonate.