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.
How many pairs of ribs compose the thoracic cage? The thoracic cage, also known as rib cage, is composed of 12 pairs of ribs. It is comprised of bony and cartilagenous structures. It is surrounded by the thoracic cavity, and it supports the shoulder girdle.