A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
Never let the Heads of your Figures, be seen erected, just in the middle of the Shoulders; but always a little turned, either to the Right or the left. This must be observed, even where they are looking up, or down, or even straight forward; it being absolutely necessary, that they should have some Attitude, to show somewhat of Vivacity, and to make it appear that they are neither Dead, nor Asleep. Further, Never Design a Figure entirely either in Profile, in Front, or even on its Backside; so as that the middle Parts, be seen rang'd perpendicularly over one another; At least, if any particular Circumstance should make this unavoidable; Remember that it be done in the Figures of Old Men; it being much more tolerable in these, than in any others, on Account of their natural Dullness, and Inactivity. Lastly, Never forget your self so far, as to repeat the same Action of the Arms, or Legs, either in the same Figure, or even in those around it: With this Proviso, however, that there be no particular Circumstance in the Subject, that may make it necessary.