According to Healthline, the human arm is composed of three bones, divided amongst two anatomical sections. The upper arm or brachium, which is the region between the shoulder and elbow joint, contains the humerus. The forearm or antebrachium contains two parallel bones, the radius and ulna.
The humerus runs down from the shoulder socket and joins the radius and ulna at the elbow. The radius runs from the elbow to the thumb side of the wrist. The ulna runs from the elbow to the pinkie side of the wrist. The radius and ulna join a collection of eight carpal bones at the hand to form the wrist, or carpus.