This sketch is one of the many sketches within the Codex on the Flight of Birds that attempt to translate the anatomy of birds to a mechanical device. Although it is not known if any actual prototypes were attempted, Leonardo’s sketches show that careful consideration was paid to devise a mechanically sound machine that mirrored the method’s used by birds to achieve flight. Leonardo’s theoretical flight machine used a combination of stirrups, levers, and pulleys to allow a human to manipulate the mechanical wing device to move in a way similar to the flapping of a bird’s wing. The sketch hightlights Leonardo's interest and knowledge in the fields of engineering, anatomy, and art by creating a mechancial device based on anatomical studies and using geometric and artistic principles to sketch his ideas.
Smithsonian National Air and Space Museum. “Leonardo Da Vinci's Codex on the Flight of Birds.” Leonardo Da Vinci's Codex on the Flight of Birds | National Air and Space Museum, 22 Oct. 2013, airandspace.si.edu/exhibitions/codex/.