The space between the parting of the lips [the mouth] and the base of the nose is one-seventh of the face.
The space from the mouth to the bottom of the chin c d is the fourth part of the face and equal to the width of the mouth.
The space from the chin to the base of the nose e f is the third part of the face and equal to the length of the nose and to the forehead.
The distance from the middle of the nose to the bottom of the chin g h, is half the length of the face.
The distance from the top of the nose, where the eyebrows begin, to the bottom of the chin, i k, is two thirds of the face.
The space from the parting of the lips to the top of the chin l m, that is where the chin ends and passes into the lower lip of the mouth, is the third of the distance from the parting of the lips to the bottom of the chin and is the twelfth part of the face. From the top to the bottom of the chin m n is the sixth part of the face and is the fifty fourth part of a man’s height.
From the farthest projection of the chin to the throat o p is equal to the space between the mouth and the bottom of the chin, and a fourth of the face.
The distance from the top of the throat to the pit of the throat below q r is half the length of the face and the eighteenth part of a man’s height.
From the chin to the back of the neck s t, is the same distance as between the mouth and the roots of the hair, that is three quarters of the head.
From the chin to the jaw bone v x is half the head and equal to the thickness of the neck in profile.
The thickness of the head from the brow to the nape is once and 3/4 that of the neck.
[Footnote: The drawings to this text, lines 1-10 are on Pl. VII, No. I. The two upper sketches of heads, Pl. VII, No. 2, belong to lines 11-14, and in the original are placed immediately below the sketches reproduced on Pl. VII, No. 1.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.