The human spine is a column of 33 total vertebrae, of which 24 are movable and free (the remainder are fused). The movable vertebrae are divided into three regions: cervical, thoracic, and lumbar. The thoracic vertebrae are located between the cervical and lumbar portions of the back. The first thoracic vertebrae spine (T1) is located in the upper part of the back.
The vertebrae themselves are numbered in descending order, and T1 is located at the top of the thoracic spine. It is located beneath, and articulates with, the seventh cervical vertebra (C7). As the thoracic vertebrae extend down the back, each bone grows relatively bigger. The lower the vertebra, the more weight it has to support – this includes not only the vertebra and cartilage above it, but the entirety of the skull as well. Comparatively speaking, T1 is the smallest of all thoracic vertebrae.
Like others, the T1 primarily encloses the spine. Several processes allow for muscular tissue attachments. Also, T1 articulates (forms a joint) with a first pair of bones in the rib cage. This articulation occurs at T1's two transverse processes. The transverse processes are areas of bone that stick out of the sides of the vertebrae.