From a to b—that is to say from the roots of the hair in front to the top of the head—ought to be equal to c d;—that is from the bottom of the nose to the meeting of the lips in the middle of the mouth. From the inner corner of the eye m to the top of the head a is as far as from m down to the chin s. s c f b are all at equal distances from each other.
[Footnote: The drawing in silver-point on bluish tinted paper—Pl. X—which belongs to this chapter has been partly drawn over in ink by Leonardo himself.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.