Long, thin curved bones which form the rib cage around the chest cavity. A horse has 18 pairs of ribs, the first 8 of which articulate both with the thoracic vertebrae and the sternum and are called vertebrosternal or true ribs. The following 10 pairs are not attached to the sternum, these are known as vertebral or floating ribs. Due to their increased mobility, the floating ribs permit the chest cavity to expand during respiration.