The spine consists of seven cervical (neck) vertebra bones, twelve thoracic (chest) vertebra bones, five lumbar (back) vertebra bones, and the sacrum (five fused vertebra). They are interconnected with small facet joints. Between each of these vertebra is an intervertebral disk which acts as a shock absorber.
The spine has several functions: providing skeletal stability to the body, allowing movement such as bending and turning, and protecting the spinal cord.
The spine is connected to the legs through the pelvis. The pelvis is a ring of bones made up of three sections. The back section of the pelvis is the sacrum. The front and side of the pelvis are made up of three segments (the Ilium, ischium, and pubis). On the sides of this ring are the cup-shaped indentions that hold the head of each upper leg (femur), forming the hip joints.
Image 1: Spinal Column Anatomy