On a sheet in the previous section of the exhibition, Leonardo stated ‘this winter of 1510 I believe I shall finish all this anatomy’. But it was not to be. In 1511 his collaborator Marcantonio della Torre died, and later that same year Milan fell into military turmoil.

Leonardo thus spent much of the period 1512 - 13 at the country villa of his assistant Francesco Melzi. Though he had lost his access to human material, Leonardo continued his anatomical work, dissecting the corpses of birds, dogs and oxen. A period of retreat during which he could have written up his earlier researches for publication was instead filled with a miscellany of new interests.

The topic that engaged Leonardo most fully was the heart of the ox (little different from the human heart). He described with great accuracy the chambers (the ventricles and atria) and the structure and functioning of the valves. But he was unable to reconcile what he observed with what he believed to be true.