Which bone is NOT considered part of the lower leg?

The sternum is not considered part of the lower leg because it is a flat bone located in the center of the chest, forming the front of the rib cage. Its primary function is to protect the heart and lungs, as well as to connect with ribs via costal cartilage. In contrast, the tibia and fibula are both long bones that make up the lower leg, with the tibia known as the shinbone and the fibula providing support and stability. The patella, commonly known as the kneecap, is also associated with the leg, specifically in the knee joint. Thus, the sternum's anatomical location and function distinctly classify it away from the structures of the lower leg, making it the correct choice in this context.