Moving from Paris, Pisa, and Oxford to London, Amsterdam, and Cambridge, this essay documents extensive collaborations between anatomists and mathematicians. At a time when no standard way to acknowledge collaboration existed, it is remarkable that in all the cases I discuss anatomists expressed in print their debt to mathematicians. The cases I analyze document an extraordinarily fertile period in the history of anatomy and science and call into question historiographic divisions among historians of science and medicine. I focus on Steno's Myology, showing how his collaboration with mathematician Viviani led to a geometrical treatment of muscular contraction and to an epistemology inspired by Galileo. The collaboration between Steno and Viviani enables us to interpret a major text in the history of anatomy, one whose implications had so far eluded historians.