Children's Slender Joints and the Proportions of Men
Why infants are thin at the joints and thick between them, and how limb-lengths differ from grown men
Continuing Part Three of the Treatise on Painting, Leonardo explains why small children are slender at the joints and thick between them: over the joints the skin is sinewy and cartilaginous, binding the bones without flesh, while the humid flesh lies between the joints and later recedes as a man grows, drawing the skin toward the bone. A further chapter compares the lengths between men and children, noting that a man has two head-lengths where a child has one, because nature builds the head, the house of the intellect, before the rest. The page ends with the opening of a chapter on the joints of the fingers. The full page is continuous text with no drawing.
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Why children are slender at the joints
Little children have slender joints and thick spaces between them; as a man grows, the superfluous flesh between skin and bone recedes so the limbs thin, while over the joints only the sinewy, cartilaginous skin remains and cannot dry out. Thus children show hollows where grown men show relief at fingers, arms and shoulders.
Skin, sinew and bone at the joints
Over the joints the skin alone, of the nature of sinew, girds and binds the bones, and the humid fleshiness lies enclosed between skin and bone in the spans between joints. Because the bones are thicker at the joints than between them, the growing flesh loses its excess and the skin draws close to the bone.
The head grows first: two head-lengths in man, one in the child
Chapter [266] finds great difference in the lengths between joints in men and children: a man has two heads from shoulder-joint to elbow, from elbow to thumb-tip, and across from shoulder to shoulder, where the child has one, because nature first composes the house of the intellect before that of the vital spirits.