The T12, or twelfth thoracic vertebra, is the bottommost and largest of the thoracic vertebrae. It is located in the thoracic, or trunk, section of the spine. It sits above L1, the first lumbar vertebra of the spine, according to InnerBody.com.
The T12 vertebra bears the most weight of all of the thoracic vertebrae. It is the strongest of these vertebrae but also the most susceptible to stress-induced injury. The body of the T12 vertebra is the largest and widest of the thoracic vertebrae, and closely resembles the bodies of the lumbar vertebrae. The arch in T12 is the thickest of the thoracic vertebrae and has facets that join the 12th pair of ribs, says InnerBody.com.