Bats have, you see, all the standard bones of the wings and legs (left). On the heel there's a bone that's special in bats, the calcar. It is an extension of the calcaneum [heel bone] and it's used to spread the interfemoral membrane. Bats that have small interfemoral membranes have small calcars or none at all. This is one. By way of contrast, the calcars of a fishing bat are so long they would overlap unless the legs are spread.

The hand of a bat as you see here has five fingers. The thumb is small and the second finger is short and doesn't reach the edge of the membrane. The third, fourth, and fifth fingers are long, and each has a metacarpal and three phalanges just as your fingers do. All microbats have only one clawed finger, the thumb, but the megabats have two. The second finger as well as the thumb is clawed in the Megachiroptera.

In the males of one family of bats, the Emballonuridae, there is a glandular pocket in the wings, so they are called "sac winged bats". In the female, this smelly sac is represented only by a line on the wing.

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