Da Vinci collaborated with Andreas Vesalius who also worked with many young artists to illustrate Vesalius’ book "De Humani Corporis Fabrica" and this launched the use of labelling anatomical features to better describe them. It is believed that Vesalius used cadavers of executed criminals in his work due to the inability to secure bodies for this type of work and dissection. He also went to great measures to utilize a spirit of art appreciation in his drawings and also employed other artists to assist in these illustrations.