The numbers, along with the corresponding letter, describe the location of each vertebrae in the spine. There are four major sections of the spine: cervical, thoracic, lumbar and sacral. The numbers for each section start with the vertebrae that are closest to the top of the spine, according to Spine-health.
The cervical spine has seven vertebrae, labeled from C1, which is nearest to the skull, to C7. These bones make up the neck and have the greatest range of motion of all vertebrae. The first and second cervical vertebrae allow a person to nod and turn his head from side to side, says the Mayfield Clinic.
The thoracic spine is below the cervical spine and has 12 vertebrae, T1 to T12. These vertebrae connect to the ribcage and have a more limited range of motion. The two lower sections of the spine have five vertebrae each. The lumbar spine consists of vertebrae L1 to L5, which are the largest vertebrae. This section of the spine supports most of the body’s weight. The sacrum consists of the five vertebrae in the sacral spine, S1 through S5, which are fused. This section connects the spine to the pelvis, the Mayfield Clinic reports.