A main work on muscular action, the “Elements of Myology,” by the Danish anatomist Niels Stensen (1638-1686) was written at a time when the teachings of Hippocrates, Erasistratus, Aristotle, & Galen were still the foundations upon which scholarly learning on the human body were built. In this work as in several other areas of research, Stensen described a structure vs. time relation as a dynamic process. From macroscopic observations of a number of muscles in several animal species, he described the contraction of compound muscles arranged in unipennate structures with an angle between muscle fibers & tendons. He found that the observed swelling of a muscle during contraction was not an argument for an expansion of its volume. Contents of this study: (1) Stensen’s Myology in HIsotrical Perspective, by Troels Kardel, M.D.; & (2) Translations of Niels Stensen’s “New Structure of the Muscles & Heart” (1663) & “Specimen of Elements of Myology” (1667) with Facsimile of First Editions” annotated by Harriet Hansen, M.A., & Aug. Ziggelaar, S.J., Ph.D. Reprint. Illus.