thoracic vertebra, one of the 12 bony segments of the spinal column of the upper back designated T1 to T12 or D1 to D12. T1 is just below the seventh cervical vertebra (C7), and T12 is just above the first lumbar vertebra (L1). The thoracic part of the spine is flexible and has a concave ventral curvature. Each vertebra has a broad thick lamina; long, obliquely directed spinous processes; and thick strong articular facets. The thoracic vertebrae are unique in having small lateral facets for articulation with the ribs. The vertebrae are separated from each other by intervertebral disks. The vertebrae become thicker and heavier in descending order from T1 to T12. Compare cervical vertebra, lumbar vertebra, sacral vertebra.
