In man the lumbar vertebrae have sometimes assumed the character of the sacral vertebrae, the sacral vertebrae presenting the aspect of lumbar vertebrae, etc.

It is quite common to see the first lumbar vertebra presenting certain characteristics of the dorsal.
Numerical anomalies of the vertebrae are quite common, generally in the lumbar and dorsal regions, being quite rare in the cervical, although there have been instances of six or eight cervical vertebrae.

In the lower animals the vertebrae are prolonged into a tail, which, however, is sometimes absent, particularly when hereditary influence exists.

It has been noticed in the class of dogs whose tails are habitually amputated to improve their appearance that the tail gradually decreases in length.

Some breeders deny this fact.
Human Tails .-- The prolongation of the coccyx sometimes takes the shape of a caudal extremity in man.