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.]