The vertebrae attached to the ribs. There are 12 of these in the human skeleton, corresponding to 12 pairs of ribs. In the spinal column, the thoracic vertebrae are located between the cervical vertebrae above, and the lumbar vertebrae below.
These vertebrae are denoted by a T (for thoracic) followed by their position along the spinal column. T1 is the top thoracic vertebra, and the numbers follow sequentially onward to T12.
The spines on the back of the vertebrae (the technical term is spinous processes) are approximately perpendicular to the bodies of the vertebrae at the top of the thoracic column, and increase in downward slope the further down the back they're located. The vertabrae themselves also increase in size in this direction.
Due to their attachment to the ribs, thoracic vertebrae are far less prone to injuries such as herniated discs. The ribs stiffen the region, allowing for considerable rotation of the torso but very little movement otherwise. Decreased mobility in this region is thus compensated for by increased safety.