Vitruvius, the architect, says in his work on architecture that the
measurements of the human body are distributed by Nature as follows:
that is that 4 fingers make 1 palm, and 4 palms make 1 foot, 6 palms
make 1 cubit; 4 cubits make a man's height. And 4 cubits make one
pace and 24 palms make a man; and these measures he used in his
buildings. If you open your legs so much as to decrease your height
1/14 and spread and raise your arms till your middle fingers touch
the level of the top of your head you must know that the centre of
the outspread limbs will be in the navel and the space between the
legs will be an equilateral triangle.

The length of a man's outspread arms is equal to his height.

From the roots of the hair to the bottom of the chin is the tenth of
a man's height; from the bottom of the chin to the top of his head
is one eighth of his height; from the top of the breast to the top
of his head will be one sixth of a man. From the top of the breast
to the roots of the hair will be the seventh part of the whole man.
From the nipples to the top of the head will be the fourth part of a
man. The greatest width of the shoulders contains in itself the
fourth part of the man. From the elbow to the tip of the hand will
be the fifth part of a man; and from the elbow to the angle of the
armpit will be the eighth part of the man. The whole hand will be
the tenth part of the man; the beginning of the genitals marks the
middle of the man. The foot is the seventh part of the man. From the
sole of the foot to below the knee will be the fourth part of the
man. From below the knee to the beginning of the genitals will be
the fourth part of the man. The distance from the bottom of the chin
to the nose and from the roots of the hair to the eyebrows is, in
each case the same, and like the ear, a third of the face.

[Footnote: See Pl. XVIII. The original leaf is 21 centimetres wide
and 33 1/2 long. At the ends of the scale below the figure are
written the words _diti_ (fingers) and _palmi_ (palms). The passage
quoted from Vitruvius is Book III, Cap. 1, and Leonardo's drawing is
given in the editions of Vitruvius by FRA GIOCONDO (Venezia 1511,
fol., Firenze 1513, 8vo.) and by CESARIANO (Como 1521).]

The arm and head.