Quotation from: The Notebooks of Leonardo Da Vinci

Written by: Leonardo da Vinci

825.

Note on the bendings of joints and in what way the flesh grows upon
them in their flexions or extensions; and of this most important
study write a separate treatise: in the description of the movements
of animals with four feet; among which is man, who likewise in his
infancy crawls on all fours.

826.