This sheet displays the full range of Leonardo’s illustrative techniques, showing the structure of the muscles of the shoulder. Pectoralis major is divided into parts to represent the lines of force along which it acts. This method reaches its logical conclusion in the drawing at top right, which is an example of Leonardo’s ‘thread model’. This technique - invented by Leonardo - reduced the muscles to single cords along their central lines of force, such that the spatial structure of an entire system can be perceived at once. RL 19003v Text adapted from Holbein to Hockney: Drawings from the Royal Collection