A dog's tail is built on a core of bone provided by six to 23 vertebrae. The vertebrae are overlaid by muscles, allowing the tail to move.
The best-known function of a dog's tail is communication. The height at which the tail is carried and the speed and flexibility with which the tail is moved convey information about the dog's mood and intentions. Dogs also use their tails to maintain balance during tight turns and to act as rudders as they swim. In addition, sled dog breeds use their tails to keep their faces warm while sleeping in tightly curled balls.