The 24 vertebral segments in the upper three regions are termed the true false( true, false ) or movable fixed( movable, fixed ) vertebrae. The pelvic segments in the lower regions are called false true( false, true ) or fixed movable( fixed, movable ) vertebrae.

The cervical and lumbar curves, which are convex concave( convex, concave ) anteriorly, are called lordotic kyphotic( lordotic, kyphotic ) curves. The thoracic and pelvic curves are concave convex( concave, convex ) anteriorly and are called kyphotic lordotic( kyphotic, lordotic ) curves

The thoracic cervical lumbar( thoracic, cervical, lumbar ) and pelvic sacral lumbar( pelvic, sacral, lumbar ) curves are called primary curves because they are present at birth. The cervical pelvic thoracic( cervical, pelvic, thoracic ) and lumbar sacral thoracic( lumbar, sacral, thoracic ) curves are called secondary or compensatory curves because they develop after birth.

The cervical thoracic lumbar( cervical, thoracic, lumbar ) curve, which is the least pronounced of the curves, develops when an infant begins to hold the head up at about 3 2 1 4( 3, 2, 1, 4 ) or 4 5 3 2( 4, 5, 3, 2 ) months of age and begins to sit alone at about 8 6 7 9( 8, 6, 7, 9 ) or 9 8 10 11( 9, 8, 10, 11 ) months of age. The lumbar cervical thoracic( lumbar, cervical, thoracic ) curve develops when the child begins to walk at about 1 0.5 2 1.5( 1, 0.5, 2, 1.5 ) to 1.5 2 2.5 3( 1.5, 2, 2.5, 3 ) years of age.

Any abnormal increase in the anterior concavity (or posterior convexity) of the thoracic curve is termed kyphosis lordosis( kyphosis, lordosis ). Any abnormal increase in the anterior convexity (or posterior concavity) of the lumbar or cervical curve is termed lordosis kyphosis( lordosis, kyphosis ).

In the articulated spine, the vertebral bodies are separated by intervertebral disks, forming the cartilaginous interver­tebral joints. These disks account for approximately one fourth of the length of the vertebral column. Each disk has a central mass of soft, pulpy, semigelatinous material called the nucleus pulposus anulus fibrosus( nucleus pulposus, anulus fibrosus ), which is surrounded by an outer fibrocartilaginous disk called the anulus fibrosus nucleus pulposus( anulus fibrosus, nucleus pulposus ).

The bodies of the typical (third through ninth third through eleventh second through ninth fourth through twelfth( third through ninth, third through eleventh, second through ninth, fourth through twelfth )) thoracic vertebrae are approximately triangular in form.

Although the size and degree of curvature of the sacrum vary considerably in different patients, the bone is normally longer, narrower, more evenly curved, and more vertical in position in males females( males, females ) than in females males( females, males ).