Human dissection was not prohibited by the Church, as is often supposed. Leonardo conducted his work quite openly – he did after all want to publish his researches – and by the end of his life he claimed to have dissected over thirty bodies.

Doctors performed autopsies to investigate the cause of a mysterious death, and public dissections were staged by the medical schools of Italy’s universities. The subjects of the latter were executed criminals, or the destitute who had died in charitable hospitals with no relatives to claim their bodies for burial.

But a mere artist could not easily obtain a human body for dissection. So at the start of his career Leonardo investigated animals instead, and the first two sheets here record his studies of dogs, monkeys, frogs and pigs. The second two sheets, however, demonstrate that Leonardo dissected a human leg as early as the 1480s. And during the 1500s, as his reputation grew, he was allowed to dissect corpses in hospitals and medical schools.