Quotation from: The Notebooks of Leonardo Da Vinci

Written by: Leonardo da Vinci

803.

You must show all the motions of the bones with their joints to
follow the demonstration of the first three figures of the bones,
and this should be done in the first book.

804.

Remember that to be certain of the point of origin of any muscle,
you must pull the sinew from which the muscle springs in such a way
as to see that muscle move, and where it is attached to the
ligaments of the bones.