Mid-back - Thoracic spine

The thoracic spine is the area between the neck and lower back that supports the chest. The shape of the thoracic vertebrae is similar to those in the lumbar spine but reduced in size. Again, just like its neighbors above and below, the disc in front separates the two vertebral bodies and the facets in back guide the motion of the spine. The discs in the thoracic spine have the same anatomy as the lumbar spine but are thinner and somewhat inflexible. The major difference between this area and the lumbar spine is that ribs attach to each thoracic vertebra and this makes this area of the spine very stiff.

The alignment of the spine differs from the neck and lower back. From front to back, the spine should be straight (a curve greater than 10 degrees would be considered a scoliosis). From the side view, the spine should have a front to back curve called a kyphosis. This curve ranges from 20-40 degrees and is important to balance out the entire spine. This curve along with the opposite curves in the neck and lower back balance the head over the pelvis. 

To better understand these conditions, please read Anatomy of the Thoracic Spine first.