By July, Leonardo had returned with the king and the French army to Milan. Here was planned a great celebration of the French victory over the Venetians. In front of the cathedral, to the delight of the hundreds of spectators, Leonardo devised a mechanical lion scaring a dragon out of an artificial lake into the beak of a cock which picked the dragon’s eyes out. After the festivities Leonardo returned to his everyday work. In time, he had a thriving workshop and as he became more and more preoccupied with his scientific explorations, his art commissions were turned over to his assistants. He did continue, however, to work on the plans for Marshal Trivulzio’s monument and in his preparatory work for this assignment he expanded his notes and drawings of comparative anatomy. This renewed interest in anatomy led him to attend a lecture in the winter of 1509. The lecturer was Marcantonio della Torre, a young man in his late twenties and one of the best-known anatomists of the times. He had been a professor at the University of Padua, but this city had fallen into the hands of the Venetians. Marcantonio was forced to flee Padua and had settled at Pavia. The two men, when they met, recognized in each other a devotion to science and they began a professional collaboration that grew into a friendship. Leonardo now developed his anatomy studies to the point where he is today recognized as the foremost medical anatomist of the Renaissance. Returning to his dissections, Leonardo now proceeded to explore the heart and system of veins in the human body. His drawings of the heart are nearly perfect. Indeed, he was probably the first to discover the endocardium membrane that sheathes the valves and sinews of the heart. Also, he pictured and described the moderator band, “the first cause of the motion of the heart.” His work on this organ led him to the doorstep of discovering the circulation of the blood—later to be carried out by William Harvey in the seventeenth century. Further, Leonardo was the first to accurately draw a representation of the _foetus_, or unborn child, in the womb of its mother, writing in his notes that, “we conclude therefore, that a single soul governs the bodies and nourishes the two.” In addition, he drew a remarkable picture of the female figure and for the first time accurately placed her organic structure. In his notes, he also pointed the way to the laws governing metabolism when he wrote, “The body of anything whatsoever that receives nourishment continually dies and is continually renewed....” By pouring wax into a hole in the skull he made the first casts of the ventricles of the brain. Several hundred years were to pass before this method was rediscovered.