Here's why:

* Bone Structure: Bats and humans have the same basic bone structure in their forelimbs. They both have a humerus (upper arm), radius and ulna (forearm), carpals (wrist bones), metacarpals (hand bones), and phalanges (finger bones).

* Muscle Arrangement: The muscles that control movement in a bat's wing are similar in arrangement and function to those in a human arm.

* Evolutionary Relationship: Bats and humans share a common ancestor, and their forelimbs evolved from a similar structure.

While the wing is adapted for flight, it still retains the basic structure of a hand, which is why it's considered analogous to the human arm.