Chap. LVI.—Of the Muscles.
The muscles of the human body are to be more or less marked according to their degree of action. Those only which act are to be shewn, and the more forcibly they act, the stronger they should be pronounced. Those that do not act at all must remain soft and flat.
Chap. LVII.—Of the Bending of the Body.
The bodies of men diminish as much on the side which bends, as they increase on the opposite side. That diminution may at last become double, in proportion to the extension on the other side. But of this I shall make a separate treatise[17].
Chap. LVIII.—The same Subject.
The body which bends, lengthens as much on one side as it shortens on the other; but the central line between them will never lessen or increase.
Chap. LIX.—The Necessity of anatomical Knowledge.
The painter who has obtained a perfect knowledge of the nature of the tendons and muscles, and of those parts which contain the most of them, will know to a certainty, in giving a particular motion to any part of the body, which, and how many of the muscles give rise and contribute to it; which of them, by swelling, occasion their shortening, and which of the cartilages they surround.
He will not imitate those who, in all the different attitudes they adopt, or invent, make use of the same muscles, in the arms, back, or chest, or any other parts.