Da Vinci based his flying machine on the structure of kites, and the wings of birds and bats. It is more evident that his used a bats wing, as it has a very similar bone structure (Fig. 1)
It is also evident that Da Vinci used kites as a inspiration, he used the idea of sporadic movement but with stability is the basis of his design, to be able to maneuver quickly but effortlessly.
Da Vinci replicated the way the bat's wing is formed by using a light wood structure, most likely pine and covered it in raw silk. It was intended as a one man machine, that used all of the body parts of the pilot, merging the two together. The pilot pedaled with his feet, like a bicycle while using his arms as stabilizers. To steer, the pilot simply looked in the direction they wanted to go, the movement of the head triggered a collection of pulleys that turned the wing bar in a certain direction.
Da Vinci was obsessed with pulleys and cogs, all of his inventions used them. He found them the easiest way to convert and transfer energy to separate mechanisms.