Dogs have an average of 319 bones in their bodies. The number varies somewhat depending on tail length, since short tails have fewer vertebrae than long tails. Some breeds, such as the great Pyrenees, also have extra bones in their hind dewclaws.
The main difference in the number of bones is in the caudal vertebrae that make up the dog's tail. There are natural differences in tail length that account for some variation. Some breeds of dogs have their tails docked, which results in the removal of caudal vertebrae. Other than tail length, the skeletal structure of various breeds is similar. Differences in bone sizes account for differences in conformation and size between breeds.