Answer:
Just like in a person's arms, in a frog's front legs are bones called the humerus, the radius and the ulna. However, a frog's radius and ulna are fused into one bone. The same is true for a frog's legs -- the femur supports its upper leg, and the bones of the lower leg, the tibia and fibula, are fused.
The frog's larger back legs consist of a femur as the strong, upper leg support, just like in humans, albeit on a different-sized scale. The back legs also consist of a fibula, as well as tibia; however, on the frog these two bones are fused together into one.