During the winter months Leonardo would relax from his work on the huge painting and his dissections to roam the country around Florence. He visited the slaughterhouses where the animals were killed and prepared for market. Here he was able to examine the hearts of animals just slaughtered and to note that the heart retained its action until the body was almost cold. He made a glass model of the aorta (the main artery leading from the heart) of an ox with which he could experiment on the flow of the blood. He intended to add to it a glass tube for one of the semilunar valves of the heart. He also experimented with a frog, dissecting its brain, heart, and entrails and noted that it ceased to twitch only when the spinal cord was severed. In his notes, he wrote, “The frog instantly dies when the spinal cord is pierced; and previous to this it lived without head, without heart or any bowels or intestines or skin; and here therefore it would seem lies the foundation of movement and life.” He was of course searching for the reasons that muscles moved and from where the impulses originated. One of Leonardo’s favorite places to visit was Fiesole where his uncle Allessandro Amadori lived. Uncle Allessandro was the brother of Leonardo’s first stepmother and, since he had loved her so much, he likewise felt an affection for Allessandro. At Fiesole, which rises over Florence in a steep ascent, Leonardo could watch the birds circling in the air below him. On these lofty heights, he would unfold his drawings of flying machines. Leonardo had progressed now to a point where an actual flight was all that was left. He had designed a sort of flying boat—a shell with wings that moved up and down and he had introduced a tail like that of a bird. He had noted that the tail of a bird acts as a rudder, a stabilizer and a brake when landing. But Leonardo’s most recent design was one that was called an _ornithopter_. It consisted of a wooden frame, two huge wings like a bat’s, a series of ropes and pulleys and a windlass, all planned with the lightest of materials. The flyer, lying prone in the frame, his feet in leather stirrups connected to the wings by pulleys, would move his feet up and down to flap the wings while, at the same time, he operated the windlass with his arms in order to guide the machine. Soon he hoped to build this machine and try it out. Meanwhile, Leonardo returned to his painting in the council chamber with impatience, for spring was approaching and the time to finally realize his dream of flying would be at hand. Aside from an assistant who had tested the pedals and windlass, no one knew of his plan to actually put his machine in the air. [Illustration: _The_ ornithopter, _one of Leonardo’s designs for a “flying machine.” By pumping his feet in the stirrups, the flyer could flap the device’s wings._]