An adult human backbone has 24 vertebral bones, referred to as the presacral vertebrae. At birth, the human spine consists of 33 individual bones. Some portions interact and fuse when an individual reaches adulthood.
An adult spine is divided into three curvatures: cervical, thoracic and lumbar. The topmost region is the cervical curve, which is made up of seven bones. The thoracic curve is the mid-spinal region, and it is composed of 12 bones. The lower back curve, called the lumbar spine, is comprised of five bones.
The sacrum and coccyx are located below the lumbar region. Prior to adulthood, the sacrum is made up of five sacral bones, while the coccyx comprises four coccygeal bones.