The Arm and Service of the Muscles.

Whether anatomical or flayed, living humans or beautiful nudes show their muscles differently; in some people, muscles are clearer than in others, and in some, small muscles are very hidden, while in others they are prominently visible. This is something the painter must take into account in scenes with many figures, to showcase the richness of his thoughts and invention. Human figures must not resemble dried-up fish nor be as lumpy as a bag of bulbs due to the swelling of muscles. Goltzius, in his depiction of Hercules, made such an error, earning his print the nickname "The Apple Bag of Goltzius" from then until now.

Additionally, it is important to note that in some actions, not all external muscles are equally visible. Where visibility might seem possible, it would be when a figure is at rest without movement or action. However, even then, many muscles are too doubtful to be clearly distinguished except by the most expert of anatomists. This necessity arises because, otherwise, the figure could not be represented without function. A general rule must be established that parts of the body contributing most to an action or deed, depending on its intensity or greatness, should be most visibly muscled and shown more clearly; this will reveal which parts bear the strength and through which limbs the action is performed, and which parts participate less or not at all. And commonly, actions are arranged accordingly.

Translation Notes:

"Goltzius" refers to Hendrick Goltzius, a noted Dutch printmaker and painter, known for muscular depictions.