Advice to the painter-anatomist on muscles
Do not make wooden nudes by displaying every bone and muscle
A full page of mirror-script under the heading "Pittura," with no diagram. Leonardo warns the anatomist-painter that too much knowledge of bones, cords, and muscles can make him a "wooden" painter if he insists on showing every one in his nudes. He advises studying how muscles clothe the bones in old and lean men, which muscles stay visible at every degree of fatness and which vanish with the least plumpness, and how, around the joints of any animal, the same muscles appear and disappear as the limbs move.
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Beware the wooden nude that shows every muscle
Leonardo cautions the painter-anatomist that too much knowledge of bones, cords, and muscles can make him a wooden painter, if he wants his nudes to display all their features at once. The remedy is to observe how muscles cover the bones in old or lean men. The aim is a living figure, not an anatomical display.
Which muscles show, and how fat and leanness change them
He directs study of how muscles fill the surface spaces between them, which muscles never lose visibility at any degree of fatness, and which lose the notice of their junctions at the least plumpness. In growing fat several muscles may merge into one, while in growing lean or old one muscle may seem to divide into several. All these particulars are to be shown especially in the spaces between the joints of each limb.
Muscles change around the joints as the limbs move
Leonardo adds that the painter must note the variety these muscles make around the joints of the limbs of any animal through the diversity of each limb's movements. On some side of a joint the muscles may become entirely lost to view. This happens through the increase or diminution of the flesh of which the muscles are composed.