A weary white horse, having carried a pilgrim and his cargo of scriptures across half the world, is led down from a Spirit Mountain to the edge of a pool. He plunges in, and the water changes him: he rises "with horns, scales," and "claws, and wings complete", no longer a beast of burden but a dragon, and from that hour "he became the chief of the" celestial dragon tribe. The wings are the last item in the list, the finishing stroke of the metamorphosis — a dragon is not fully a dragon until the wings are on. This is the motif Thompson filed as the wings of the dragon: not a deed but a feature, the pinioned back that lets the water-serpent take the sky.

The witness is a chapter of Myths & Legends of China (a compilation of Chinese myth published in 1922), retelling the great pilgrimage-romance in which a white horse named Pai Ma is the least of the travelling company and the last to be rewarded. He alone among Chinese dragons is made rather than born winged, and the served text lingers only a clause on the moment — the pool called "the Pool of Dragon-transformation", a single splash, the finished shape. Elsewhere in the same tradition the wings are a standing part of the anatomy rather than an event: the ordinary dragon is drawn with a horse's head and a snake's tail and membranes at the sides, so that the winged and hornless and scaly kinds shade into one another. Here the shelf shows the feature being born instead of merely described.

Thompson's authorities reach past China — the apparatus points also to a study of the dragon by Smith — and Milton's winged serpent-shapes and Virgil's monsters of "foul wing" hang nearby, unquoted, on the same shelf. But it is the Chinese pool that gives the plainest picture: the wing as the credential of the dragon, the thing that turns a patient animal into a lord of the clouds. What is it about a wing that a horn or a scale cannot supply — why must the water-creature, to be complete, first be given the air?