Number of vertebra constant in (DNB June 2009)
a. In human anatomy, the vertebral column usually consists of 24 articulating vertebrae and 9 fused vertebrae in the sacrum and the coccyx.
b. It is situated in the dorsal aspect of the torso, separated by intervertebral discs. It houses and protects the spinal cord in its spinal canal, and hence is commonly called the spine, or simply backbone.
c. There are normally thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygealbones that form the tailbone.
d. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy.
e. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another.
f. The number of cervical vertebrae is, however, very rarely increased or diminished.