Recto: The bones of the foot. Verso: The bones and muscles of the arm

Studies of the foot, examining the articulation of the ankle joint, and the role of the ‘sesamoid bones’ at the ball of the foot, the subject of the details in pale ink. Those two small bones, embedded in the flexor tendon of the big toe, improve the efficiency of that tendon, and thus give greater strength in walking or running. The haphazard nature of this sheet – compiled partly the other way up, in different inks over a period of time – emphasizes the work-in-progress nature of Leonardo’s anatomical notes. Leonardo’s interest in the motions of the shoulder and arm continues on the verso of this sheet, which investigates the rotation of the lower arm and hand. The upper two drawings show the arm and shoulder from above, first with the bones in their natural positions and then separated out to demonstrate their articulation. The only muscle shown is biceps, with its double origin on the shoulder blade (scapula): Leonardo discovered that biceps has two actions, both bending the arm at the elbow and rotating the forearm to turn the palm upwards (supination) – it would be two centuries before this observation was repeated. The lower drawings study the muscles in the forearm that turn the arm to direct the palm downwards (pronation). Text adapted from Leonardo da Vinci: A life in drawing, London, 2018