A Treatise on Painting/Chapter 46
Chap. XLVI.—The Extension and Contraction of the Muscles.
The muscle at the back part of the thigh shows more variety in its extension and contraction, than any other in the human body; the second, in that respect, are those which compose the buttocks; the third, those of the back; the fourth, those of the neck; the fifth, those of the shoulders; and the sixth, those of the Abdomen, which, taking their rise under the breast, terminate under the lower belly; as I shall explain when I speak of each.