The axial skeleton: spine, skull and rib cage
The vertebral column has 33 vertebrae in five groups: 7 cervical (neck, medium size), 12 thoracic (chest, larger), 5 lumbar (lower back, the largest), 5 sacral (broad and fused together) and 4 coccygeal (small and fused together). So 7 + 12 + 5 + 5 + 4 = 33. This count is made before the sacral and coccygeal vertebrae fuse. The column is the main support of the body, it protects the spinal cord, and it lets the head and upper body move. Each vertebra has a thick centrum in front, two transverse processes at the sides, and a neural arch behind. The arch surrounds the neural canal, where the spinal cord runs, and carries a neural spine pointing backwards and down. The skull has a cerebral part of 8 bones joined firmly at their serrated edges round the brain, with the foramen magnum at its base, and a facial part of 14 bones that form the jaws and the places for the ears, eyes and nose. The rib cage is a slightly cone-shaped case. In front is the sternum. Behind are 12 pairs of curved ribs joined to the thoracic vertebrae. The first 10 pairs reach the sternum, directly or through cartilage, and the last two pairs are short and do not reach it: these are the floating ribs. The rib cage protects the heart and the lungs.
| Region | Vertebrae | What marks it |
|---|---|---|
| Cervical | 7 | neck; medium size |
| Thoracic | 12 | chest; ribs attach; larger |
| Lumbar | 5 | lower back; the largest |
| Sacral | 5 | broad; fused together |
| Coccygeal | 4 | small; fused together |
| Part | Position | Job |
|---|---|---|
| Centrum | thick part in front | carries the weight |
| Transverse processes | one on each side | a place where a rib joins (in the chest) |
| Neural arch and canal | behind the centrum | surrounds and protects the spinal cord |
| Neural spine | behind, pointing down | a bony ridge you can feel under the skin |
A spine of paper squares. With a grown-up, cut 33 small paper squares and colour them: 7 blue, 12 red, 5 green, 5 yellow and 4 grey. Line them up in that order. Then glue the 5 yellow squares into one long piece and the 4 grey squares into another. Count the separate pieces that are left, and write what the picture shows about the adult spine. Then take a deep breath with your hand flat on your own ribs, and write what you feel move and which organs the ribs protect.