The Da Vinci Notebooks at sacred-texts.com
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.
172:137 : 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.