The text discusses how muscles adapt according to the force exerted, such as when clenching a fist or holding an object. It highlights the observable changes in muscles around the chest, abdomen, and other areas, explaining how they attach and interact. It also mentions muscles that behave independently, such as those in the lips and forehead, and suggests guidance for understanding muscle behavior in artistic practice.
Muscles and the Service of Muscles.
According to the will, whether it is strong or gentle, the muscles must adjust equally in their display. For instance, when someone clenches their fist tightly or holds something with force, the muscles of the forearm will become thicker. This is because, when the hand is drawn in and pulled, it seems slightly to retreat and swell; upon opening the hand again, the shape of the arm returns to its previous form.
This change in the muscles is mainly observed around the chest and abdomen, thighs, buttocks, back, spine, shoulders, and neck. This occurs because little motion can be made in these areas without causing changes in the muscles. This is easy to understand when noting that the heads of most muscles begin in those places and are connected and firmly attached with their tendons or cords to less and more distant parts.
There are also muscles that can move on their own without assistance or change, such as the lips, forehead, and similar areas, which move directly with the skin. Because these muscles do not need to move the limbs they are in, they are made without tendons; thus, they are quite different in arrangement from other muscles. We will provide some precise instructional guidance for the practice of painting; we will proceed with explaining the muscles in cases of action.