This is a matching pair of two sets of human arm bones, articulated at the elbow joint with aluminum hinges. Three bones compose the skeletal structure of the human arm: the humerus, the radius, and the ulna. The radii are missing from both sets. The humerus is the larger bone, it connects the elbow to the shoulder through the upper arm. The radius and ulna are the two bones of the forearm and connects to the wrist on the pinky finger side. The hinges on these specimens "explode" the ulna away from the humerus, providing a clear view of the coronoid fossa and the trochlea on the humerus.