Final answer:
Homologous structures like the wings of bats and birds, the foreleg of a horse, the flipper of a whale, and the human arm all share a similar bone structure, indicating a common ancestor despite different functions.
Step-by-step explanation:
Structures that can "easily" be compared to the human arm are known as homologous structures, which reflect a common evolutionary origin. For example, the wings of bats and birds, the foreleg of a horse, the flipper of a whale, and the human arm are all homologous structures. The human arm consists of 30 bones: the humerus in the upper arm, the ulna and radius in the lower arm, eight carpal bones in the wrist, five metacarpals in the hand, and 14 phalanges in the fingers. Despite the difference in function—such as flying, swimming, or grasping—these structures share a similar basic pattern of bones inherited from a common ancestor.