Anatomical studies of the shoulder

“Leonardo then applied himself, even more assiduously, to the study of human anatomy, … [and] he did meticulous drawings in red chalk and pen of bodies he had dissected himself. He showed all the bone structure, adding in order all the sinews and covering them with the muscles: the first attached to the skeleton, the second that hold it firm and the third that move it. In the various sections he wrote his observations in puzzling characters (written in reverse with the left hand)…” (Vasari).

At the top right is a diagram of the right shoulder in which Leonardo has reduced the muscles to a cord representing the direction of force of each muscle. He thus made it clear how the muscle system works in a way that cannot be seen in nature.