Chief among the many adaptations of the bat for powered flight is the bat wing, and the flapping flight style that uses muscle power to generate lift and thrust. The bat wing evolved from the forelimbs of a terrestrial mammalian ancestor. The mammalian forelimb is exceedingly mobile because the shoulder joint between the scapula (shoulder bone) and the humerus (upper forelimb bone) is loosely held together with muscles. This allows for actual rotation of the arm around the shoulder joint in many species. Primates have this mobility, and so do bats.
The taxonomic name of the bats, order Chiroptera (meaning, “hand-
It is richly supplied with blood vessels. The region of the patagium that stretches from the sides of the body and the hind limbs to the arm and the fifth digit is called the plagiopatagium. Other portions of membrane extend from the shoulder to the pollex (first digit) along the anterior portion of the wing (propatagium), between the fingers (the chiropatagium), and from the hind limbs to the tail (the uropatagium, also called the interfemoral membrane). The wing operates on an airfoil design, with the flexible membrane segments changing shape to produce variable pressure gradients along the wing surface that results in variable amounts of lift and thrust. The bats’ fine control of the shape of the patagium gives them a maneuverability that cannot be matched by birds.
Bat flight is controlled by seventeen different pairs of muscles. Three different muscles provide power for the downstroke. Another three muscles execute the upstroke. This is very unlike birds, where two pairs of muscles provide the power for the depression and elevation of the wings. The sternum (breastbone) in bats is not particularly well developed, while in birds it is very prominent with a well-
The hind limb possesses a bony spur unique to bats called a calcar that projects inwardly from the tibia. This bone attaches to the uropatagium and functions to keeps the tail portion from flapping during flight. The legs can also form a pouch out of the uropatagium used for catching insects. In most bats, the hind limbs have rotated 90° outwardly and assumed a reptilian-