spinal column, bony column forming the main structural support of the skeleton of humans and other vertebrates, also known as the vertebral column or backbone. It consists of segments known as vertebrae linked by intervertebral disks and held together by ligaments. In human beings, the spinal column of the child contains more vertebrae than the adult, in whom a number become fused into two immovable bones, the sacrum and the coccyx, forming the back of the pelvis. The 24 movable vertebrae are the 7 cervical (neck), 12 thoracic (back of chest), and 5 lumbar (loin). The remaining vertebrae include 5 fused sacral, and between 3 and 5 fused caudal. Each vertebra has a somewhat cylindrical bony body (centrum), a number of winglike projections, and a bony arch. The bodies of the vertebrae form the strong but pliable supporting column of the skeleton. The arches are positioned so that the space they enclose is in effect a tube, the vertebral canal. It houses and protects the spinal cord, and within it the spinal fluid circulates. Ligaments and muscles are attached to various projections of the vertebrae. The 12 pairs of ribs that make up the front of the chest are linked to the thoracic vertebrae. The spine is subject to abnormal curvature, injury, infections, tumor formation, arthritic disorders, and puncture or slippage of the cartilage disks. Scoliosis is one relatively common disease which affects the spinal column. It involves moderate to severe lateral curvature of the spine, and, if not treated, may lead to serious deformities later in life.