There is one radius (R1) and one ulna (U1); these are the two bones that connect the wrist and elbow. There are two humerus bones (H1 and H2). The humerus connects the shoulder and the elbow.

For example, the humerus, radius and ulna work with your biceps and triceps to curl or extend your arm. Having many joints allows for complex fluid movements so we can do things like kick a ball ...