vertebra /vur″təbrə/ pl. vertebrae [L, joint] , any one of the 33 bones (26 in the adult) of the spinal column, comprising the 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (1 in adult), and 4 coccygeal vertebrae (1 in adult). The vertebrae, with the exception of the first and second cervical vertebrae, are much alike and are composed of a body, an arch, a spinous process for muscle attachment, and pairs of pedicles and processes. The first cervical vertebra is called the atlas and has no vertebral body. The second cervical vertebra is called the axis and forms the pivot on which the atlas rotates, permitting the head to turn. The body of the axis also extends into a strong, bony process (the dens).
