Vertebrae

Cervical vertebrae are the smallest of all vertebrae and differ from others, in that they have an artery which passes through a foramen of each of transverse processes. The first cervical vertebra (C1) connects the spine to the skull. The thoracic vertebrae are situated between the cervical and lumbar sets of vertebrae within the vertebral column. They are of intermediate size and are distinguished by the presence of facets which connect them to the ribs. The lumbar vertebrae are the largest five vertebrae of the spine. In humans, some individuals have four, while others have six lumbar vertebrae. The fifth vertebra is characterized by being located deeper in front. Sacral vertebrae fuse to comprise the sacrum, a large bone at the base of the vertebral column, which connects to the hip bones. In humans, sacral vertebrae begin to fuse approximately at the age of 16, a process which is completed by the age of 35. In addition, the sacral intervertebral discs ossify into the adulthood and as a result, the newly forming sacrum bone does not include intervertebral discs.