"Human reproduction had always fascinated him. In 1512, at the height of his powers, he drew The Fetus in the Womb. 'The womb, split open like a burst seed-case, reveals the coiled fetus, shaped into compelling roundness by the rhythmic curves of his pen,' wrote Leonardo authority Martin Kemp in Nature. One of his most famous anatomical drawings, it depicts what he called 'the great mystery,' a mystery in many ways more profound than the enigmatic smile on his Mona Lisa. With The Fetus in the Womb, the study of science, medicine, and human reproduction were brought to bear on that mystery.
'The navel is the gate from which our body is formed by means of the umbilical vein,' he wrote. What Leonardo could not have imagined as he examined the umbilical cord attaching the fetus to the mother was that it is a treasure trove of stem cells--cells with regenerative powers that someday may eradicate any number of diseases. Stem cells that already have saved the lives of people with diseases of the blood and bone marrow. People like Molly Nash."