These drawings of the muscles of the back, from 1508 - 09, were probably made to show artists how to differentiate between the various shapes seen on the back of a figure. We can tell that the drawings are not of a living model
because they follow the methods of Leonardo's drawings of his dissections of the body. In the drawings of the arm, for example, the divisions of the deltoid muscle have been exaggerated slightly and reflect Leonardo's methods of
dissection: when muscles are put back together after dissection, the divisions remain rather more distinct than is normal.
This type of carefully outlined muscle structure was followed by Michelangelo in his drawings, which resulted in the wonderful realism and solidity of the great figures in the Sistine Chapel. Although Michelangelo could be critical of Leonardo's achievements, he must have been keenly aware of the enormous strides Leonardo had made in the depiction of the human body according to scientific knowledge rather than by observation only.