The phylum Chordata is a taxonomic group. All animals which have a  spine, or backbone, are classified in the phylum Chordata. There  are three subphylums in Chordata: Uroch â¦ ordata (tunicates),  Cephalachordata (lancelets), and Vertebrata (vertebrates).
The 12 vertebrae in the upper back make up what is known as the thoracic spine. They curve outward and inward to provide structure for the rib cage. The bones provide structure and flexibility for the body, while protecting the spinal colu... Read More.
This portion of the spine is meant to support the rib cage and provide proper posture for the body. The 12 vertebrae that make up the thoracic spine, commonly referred to as T1-T12, each have two facet joint sets â one set on the top and one set on the bottom â that are responsible for providing the middle back with flexibility and strength.