Final answer:
There are two pairs of ribs, specifically the 11th and 12th pairs, that are classified as floating ribs and do not have any attachment to the sternum. These ribs terminate within the musculature of the lateral abdominal wall.
Step-by-step explanation:
The human rib cage, also known as the thoracic cage, is part of the axial skeleton and provides protection for the thoracic organs such as the heart and lungs. The ribs are classified into different groups based on their attachment to the sternum, a flat bone located at the front of the rib cage. Ribs numbered 1-7 are referred to as true ribs (vertebrosternal ribs) and they attach directly to the sternum via their costal cartilage. Ribs 8-12 are known as false ribs (vertebrochondral ribs). The costal cartilages from these ribs either attach indirectly to the sternum via the costal cartilage of the next higher rib or not at all. Specifically, ribs 8-10 are attached to the cartilage of the next higher rib and are not directly connected to the sternum. The floating ribs (vertebral ribs), which are ribs 11-12, do not have any attachment to the sternum. They are short ribs whose costal cartilages do not connect to the sternum or to other ribs' cartilage. Instead, they terminate within the musculature of the lateral abdominal wall. Therefore, there are two pairs of ribs, the 11th and 12th pairs, that do not have any sternum attachment.