 A succession of researchers proceeded to refine the body of anatomical knowledge, giving their names to a number of anatomical structures along the way.The 16th and 17th centuries also witnessed significant advances in the understanding of the circulatory system, as the purpose of valves in veins was identified, the left-to-right ventricle flow of blood through the circulatory system was described, and the hepatic veins were identified as a separate portion of the circulatory system.The lymphatic system was also identified as a separate system at this time.