Final answer:
The external oblique muscle overlies the lateral aspects of the lower ribs, specifically the false ribs 8-12, including the floating ribs 11 and 12.
Step-by-step explanation:
The structure that overlies the lateral aspects of the lower ribs is the external oblique muscle. This flat, superficial abdominal muscle, with fibers that run in a direction diagonal to the midline of the body, helps form the lateral part of the abdominal wall. It serves an essential role in the movement and support of both the abdominal wall and the contents of the abdominal cavity.
The lower ribs specifically referred to are typically the false ribs, which include vertebrochondral ribs 8-12. These ribs are called false ribs because their costal cartilages either attach indirectly to the sternum via the costal cartilage of the next higher rib (for ribs 8-10), or they do not attach to the sternum at all, which is the case for ribs 11 and 12, also known as floating ribs.