Final answer:
Under each rib, from top to bottom, the order is costal cartilages, rib bone, intercostal blood vessels and nerve, and the xiphoid process.
Step-by-step explanation:
The structures found underneath each rib in descending order are as follows: starting from the uppermost portion, we have the costal cartilages connecting the ribs to the sternum or to the cartilage of the rib above. Below the costal cartilages are the ribs themselves, which are curved, flattened bones numbered 1-12. Beneath the ribs, there is the costal groove, which carries the intercostal blood vessels and nerve.