A timeline of the evolution of medical knowledge. The upper part of the figure shows the conceptual evolution of di­seases from a descriptive clinical phase of external findings (signs, symptoms) to that of an investigative basic research phase of internal organ involvement and pathophysiology. The long grey arrow in the center of the figure represents a time line of the classical histori­cal periods shown in the light grey boxed arrows immediately below this arrow. The bottom smaller grey arrows of the figure represent the corresponding stages in the evolution of medicine from its origins as folk and priestly medicine in an­tiquity to its present therapeutic curative stage. The progress of medical knowledge by the va­rious basic science disciplines during each stage is shown in the black boxes with white italic lettering just below their respective historical period. The lightening symbol at the center of the figure is to highlight the Enlightenment period covered in this article when anatomy transitioned into physiology and chemistry was just begun.