Which bone is not associated with the arm?

The scapula, commonly known as the shoulder blade, is not categorized as a bone directly associated with the arm itself, but rather serves as an attachment point for the arm at the shoulder joint. It plays a crucial role in shoulder mechanics and is involved in the movement of the arm; however, it does not extend down the arm nor is it part of the arm's bony structure.

In contrast, the humerus, radius, and ulna are the three primary bones that make up the arm. The humerus is the long bone of the upper arm, connecting the shoulder to the elbow. The radius and ulna are the two bones of the forearm, running from the elbow to the wrist. These bones collectively facilitate the range of motion and functionality of the arm, whereas the scapula's involvement is more about connecting the arm to the torso rather than being a part of the arm itself.