33 vertebrae
The vertebral column of a child has 33 vertebrae: 7 cervical in the neck, 12 thoracic that carry the ribs, 5 lumbar in the small of the back, 5 sacral and usually 4 coccygeal. In an adult the sacral ones have fused into the sacrum and the coccygeal ones into the coccyx, leaving 26 bones.
The vertebral column from the side, its regions coloured: cervical, thoracic, lumbar, sacrum and coccyx, after Gray's Anatomy, 1918, figure 111Wikimedia Commons, Henry Vandyke Carter, Public domain (Gray 111 - Vertebral column-coloured.png)
The vertebrae grow larger from the neck down, since each carries the weight above it. The column is about 70 cm long in a man and 60 cm in a woman. It shields the spinal cord and lets the trunk bend and turn. This model shows the coccyx joined to the sacrum.
The top two vertebrae carry the head. The atlas holds the skull and lets it nod. The axis has a peg that rises into the ring of the atlas, and the atlas turns around it when you shake your head.
The axis, the second cervical vertebra, from above, with the dens that rises into the ring of the atlas, Gray's Anatomy, 1918, figure 87Wikimedia Commons, Henry Vandyke Carter, Public domain (Gray87.png)
Sources
- Susan Standring (ed.), Gray's Anatomy, 42nd ed. (2020), chapter on the back.
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