In the innermost bend of the joints of every limb the reliefs are
converted into a hollow, and likewise every hollow of the innermost
bends becomes a convexity when the limb is straightened to the
utmost. And in this very great mistakes are often made by those who
have insufficient knowledge and trust to their own invention and do
not have recourse to the imitation of nature; and these variations
occur more in the middle of the sides than in front, and more at the
back than at the sides.