Arm is the upper limb of a human being. Properly, the arm is only the part between the shoulder and the elbow. The portion of the arm below the elbow is the forearm.
The arm contains one large bone, the humerus. Shoulder muscles are attached to its upper portion. Two flexor muscles bend the upper limb at the elbow. These are the biceps brachii and the brachialis. Two extensor muscles, the triceps brachii and the anconeus, straighten the upper limb. The forearm contains two bones, the radius and the ulna. Attached to these are 19 muscles that move the wrist and fingers.
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Scientists sometimes call the forelimbs of animals arms. Each kind of animal has arms specially suited to its own needs. However, all arms follow the same basic pattern. The wings of birds and bats, the flippers of seals and whales, and the fins of some fish are all variations of the arm. Because of the complex functional capabilities of their hands, human beings can use their arms for many more purposes than can any other animal.
