More information about the spine

The 12 vertebrae of the chest, or thorax (and so called thoracic vertebrae), have joints at the side where the ribs are attached.

Below the thoracic vertebrae are the five lumbar vertebrae. These are much larger, with big bony bodies and correspondingly large intervertebral discs (which is what you would expect, since they need to bear the transmitted weight of the upper body to the pelvis and hence to the lower limbs). The bottom five fused vertebrae making up the sacrum form the back part of the pelvis by joining with bones called the iliac bones at the so-called sacro-iliac joints. Running from the end of the sacrum are three or four small vertebrae, fused together, forming the coccyx - which is what is left of what used to be our tail.

During development as a foetus the spine is curved in the shape of the letter C. This changes firstly as the baby starts to lift its head, so that the vertebrae in the neck adopt a slightly reversed curve; the same happens with the lumbar vertebrae when we start to stand upright.

Although the amount of movement each vertebra can make in relation to its neighbours might seem limited there is the freedom for a degree of flexion both forwards and from side to side, and some rotation, and the vertebrae move together so the spine as a whole has considerable mobility, though this is slightly variable in different parts - there is much more flexion in the neck and the lumbar region then there is in the thorax for example.