While human dissection was not prohibited by the Church, as is often supposed, at first Leonardo had little access to human material. Most of his early anatomical studies were therefore based on traditional beliefs or animal dissection. This drawing summarises Leonardo’s initial understanding of the major organs and vessels, with the arteries arising at the heart and the veins arising at the liver. The depiction of the internal organs superimposed on the external form of a living human was common in earlier anatomical illustration.