In kneeling down a man will lose the fourth part of his height.
When a man kneels down with his hands folded on his breast the navel will mark half his height and likewise the points of the elbows.
Half the height of a man who sits—that is from the seat to the top of the head—will be where the arms fold below the breast, and below the shoulders. The seated portion—that is from the seat to the top of the head—will be more than half the man’s [whole height] by the length of the scrotum.
[Footnote: See Pl. VIII, No. 2.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.