vertebral column, the flexible structure that forms the longitudinal axis of the skeleton. In the adult it includes 26 vertebrae arranged in a straight line from the base of the skull to the coccyx. The vertebrae are separated by intervertebral disks. They provide attachment for various muscles such as the iliocostalis thoracis and the longissimus thoracis that give the column strength and flexibility. In the adult the five sacral and four coccygeal vertebrae fuse to form the sacrum and the coccyx. The average length of the vertebral column in men is about 71 cm. The cervical part measures about 12.5 cm, the thoracic part about 28 cm, the lumbar part about 18 cm, and the sacrum and the coccyx about 12.5 cm. The vertebral column in women measures approximately 61 cm. Several curves in the column increase its strength, such as the cervical, thoracic, lumbar, and pelvic curves. The cervical curve is convex ventrally from the apex of the dens to the middle of the second thoracic vertebra and is the least marked of all the curves. The thoracic curve, concave ventrally, starts at the middle of the second and ends at the middle of the twelfth thoracic vertebra. The lumbar curve, more pronounced in women than in men, begins at the middle of the last thoracic vertebra and ends at the sacrovertebral angle. The pelvic curve starts at the sacrovertebral articulation and ends at the point of the coccyx. The thoracic and the sacral curves constitute primary curves, present during fetal life; the cervical and lumbar curves constitute secondary curves, which develop after birth. Also called spinal column, spine. See also vertebra, vertebral canal.
