The term 'Back Bones' refers to the three bones that make up the spine: the sacrum (SACRA), the ulnae (ULNAE), and the VERTEBRAE (VERTEBRAE). The sacrum is a triangular bone at the base of the spine, located between the two hip bones. The ulnae are two long bones in the forearm, located on either side of the radius. The VERTEBRAE are the 33 bones that make up the spinal column, which provide support and protection for the spinal cord. Together, these three bones form the backbone, which is essential for providing structure and support to the body.