A tooth(plural teeth) is a small, calcified, whitish structure found in the jaws(or mouths) of many vertebratesand used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness. The cellular tissues that ultimately become teeth originate from the embryonic germ layer, the ectoderm. The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammalshave deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleostfish, however, the teeth are attached to the outer surface of the bone, while in lizardsthey are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligamentsto the hoops of cartilagethat form the jaw.