The term 'A Bone in the Arm' refers to the four bones that make up the human arm: the ULNA, RADIUS, humerus, and ulnar. The ULNA is the larger of the two forearm bones and is located on the medial side of the arm. The RADIUS is the smaller of the two forearm bones and is located on the lateral side of the arm. The humerus is the bone of the upper arm and connects the shoulder to the elbow. The ulnar is a small bone located near the elbow joint. Together, these four bones form the structure of the human arm.