When the arm is bent at an angle at the elbow, it will produce some angle; the more acute the angle is, the more will the muscles within the bend be shortened; while the muscles outside will become of greater length than before. As is shown in the example; d c e will shrink considerably; and b n will be much extended.
[Footnote: See Pl. XIX, No. 2.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.