Forget Geometry, Art has the upper hand.
Drawings are most meaningful when they disagree with theory.
Head/body ratio is larger in children,
Mother and son have had their head drawn at approx. same size.
Beware of the dangerous facial proportions rules ("drawing exactitude is never truth") because size of ear, nose and mouth are more dependent on head orientation, than on human anatomy.
On the Fabric of Human Body (Andreas Vesalius makes no bones about osteology).
The average human has about one testicle and one breast.
A fugitive from the law of averages. Forget science : Art has the upper hand.