Finland, have also reported a decline. Most likely, this development stems from a change in so­ called environmental risk factors. Volume II of this handbook deals further with the structure and function of the circulation and con­ sequently addresses the basic physiological and anatomical elements which are ultimately responsible for the pathological and anatomical changes in the arterial system. While not specifically devoted to the description of disease, this volume nevertheless touches on rele­ vant pathogenetic and etiologic mechanisms. More than a century ago the pathogenesis of atherosclerosis in its initial phases had been described by VIRCHOW. He made endothe­ lium the centerpiece of his observations. The morphology of the endothelium and its function playa key role in the manifestations of atherosclerosis. Our knowledge about the function of these cells have yielded important insights.