The wings of prehistoric reptiles were wing membranes between the modified front limbs and the chest. There were four fingers in each of the forearms. Three of them ended in claws, and the fourth, which stretched the wing membrane, was elongated. There were a lot of nerve endings on the wings, with which they continuously collected information about their flight status. When they did not fly, they were able to turn away their fingers in any direction, so they could roll up the wings after landing.

Pterosaur wing. Propatagium: stretches between the shoulder and the wrist; brachiopatagium: the main wing surface, stretches between the wing finger and the ankle; uropatagium: stretches between the two hind limbs. Illustration by Mark Witton, 2013.

Pterosaur wing vs. bat wing

Bats’ wings have many similarities to that of Pterosaurs. It also consists of skinfolds stretched between the body and the forearm. An important difference is that in case of bats, all the fingers except the thumb are elongated, therefore four are involved in stretching and controlling the wings. Photo by Salix, 2011.
The largest flying vertebrates with wing membranes today are represented by flying foxes. The wingspan of the large, the golden-crowned and the indian flying foxes can reach 1.5 m, and they weigh over 1 kg.