The lumbar and thoracic spine are two of the four designated regions of the human spinal column. The thoracic spine, the largest region of the four, runs through the middle back. Below it is the lumbar spine.
The thoracic region consists of 12 vertebrae, increasing in size as it descends the body. The vertebrae have abbreviated names between T1 and T12, and are typically larger than the cervical bones above the thoracic region. The rib bones attach to the thoracic vertebrae, creating a protective system for the vital organs of the abdomen.
The lumbar region, made up of five vertebrae, are designated L1 through L5. As with the thoracic region, the lumbar vertebrae are larger than their precedents, designed to carry the majority of the body's weight. The lumbar spine is more flexible than the thoracic, as it is not tied into the ribs; only the cervical spine is more flexible than the lumbar.