The desire to fly is expressed in the many studies and drawings. His later journals contain a detailed study of the flight of birds and several different designs for wings based in structure upon those of bats which he described as being less heavy because of the impenetrable nature of the membrane. There is a legend that Leonardo tested the flying machine on Monte Ceceri with one of his apprentices, and that the apprentice fell and broke his leg. Experts Martin Kemp and Liana Bortolon agree that there is no evidence of such a test, which is not mentioned in his journals.