For the first time in the Codex a bat appears, an ideal model, according to Leonardo, for constructing a flying machine.
He was not able to observe or study the bat in flight as he did with the kite, because the bat is too fast for the human eye, and in Leonardo’s day there were obviously no instruments to record it and slow it down.
On the other hand, the anatomical observation of the animal showed him that the membrane of the bat’s wing provides a continuous surface and a good support, and this merits being copied.
Next to that of the bat are drawings of other birds, all to be taken as models for the flying machine.