The text explains how the positioning of the body affects the appearance and order of the muscles and skin. When the body bends, muscles can be concealed or exposed, changing their natural form and order. These concepts help artists understand muscle structure for more accurate depiction in art.
Method for Learning
When one side is bent, one of the breasts approaches the hip on the bent side, while the other breast moves away to the opposite side; then the skin stretches over the extended side, and reveals the muscles it covers, almost in the same order as can be seen on a flayed figure; whereas on the bent side, the skin swells, the muscles blend together and appear only as large, formless folds of flesh. It is the same with the abdomen and the muscles called "straight," which are between the navel and the hollow of the stomach; these muscles, when the body is bent backward, extend and appear in their natural order; but when the body leans forward, they contract instead, and lose their shape entirely.