VII. On the Proportions and on the Movements of the Human Figure: 332.
332.
On the central point of the whole body.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.