There are 5 groups in the vertebral column. In order they are called
1) Cervical
2) Thoracic
3) Lumbar
4) Sacrum
5) Coccyx
The 4th group contain 5 bones and once you are in the adult phase, roughly at about 26 years, the 5 bones fuses into one bone which shrink the number of bones the vertebra column have but but does not lose in size.
not a 100 % sure hope this helps