The vertebral column extends from the skull to the pelvis and forms the major axial support of the body. It functions to support the head, trunk and arms, and to transmit the weight of these parts to the legs through the pelvic girdle. Additionally, it surrounds and protects the fragile spinal cords while allowing the spinal nerves to issue from the cord via opening between adjacent vertebrae.

The vertebral column is far from being a rigid supporting rod: 24 single bones (vertebrae) and 2 composite, or fused, bones (the sacrum and coccyx) are connected in such a way as to provide a flexible curved structure. Click on the "right side" button to see the curvature.
These 24 vertebrae are separated by pads of fibrocartilage, intervertebral disks, that cushion the vertebrae and absorb shocks.

Observe the curves in the vertebral column when viewed from the side.

Identify

the cervical curve,

the thoracic curve,

the lumbar curve

and the sacral curve.

We stand and move about on two legs, and our hands and arms are free for other activities. Being bipedal, however, creates problems with respect to balance. The weight of the body must remain centered over the feet, or we fall over. The double S curve of the human vertebral column does just this, and reduces the muscle action required to maintain balance to a minimum. These curvatures also increase the strength, resilience and flexibility of the spine, making it function like a spring rather than as a rod. At birth the vertebral column is arched as in quadrupeds. At approximately the third month after birth, when the infant begins to hold its head erect, the cervical curve develops. Later, when the child sits up, stands and walks, the lumbar curve develops.