The tail of a dog is an extension of its spine and is composed of individual bony segments called vertebrae. A tail may contain from six to 23 vertebrae.
A versatile set of muscles enables various segments of the tail to move in different ways. The tip, for example, is capable of finely graded movements so that it can move from side to side, up and down or be drawn between the rear legs. Caudal muscles in the lumbar, sacrum and tail vertebrae are attached to the tail by tendons. Dogs communicate with their tails. An upright tail signifies alertness and confidence and is comparable to a friendly smile in a human.