The text discusses the characteristics of young children's limbs and joints, illustrating how their physical form is portrayed in art. It contrasts children's features with those of adults, noting children's plumpness and looser joints compared to the more defined structures of adults. References to Leonardo da Vinci highlight the observations on anatomy and growth.
THEORY
All these various characteristics of children, who still retain the plumpness and size of youthful limbs, can be seen in the antique marbles of Rome.
Young children should be depicted with quick movements and body contortions when seated. Standing, they should appear timid and fearful. Leonardo da Vinci, Chapter 61.
All young children have loose joints and the spaces between them are larger: this occurs because, at the joints, there is only skin and no other flesh except for a nervous nature that binds and connects the bones together, so that the soft and fleshy part is found between each joint enclosed by the skin and the bones. But because in the joints the bones are larger than in the same joints, the flesh, as the person grows, leaves this excess that would remain between the bones and the skin, so that the skin approaches closer to the bone, and makes the limbs more slender around the joints, because where there is no cartilage and nervous skin, it cannot wither, and without withering, it does not diminish. Therefore, for these reasons, young children are weak and lean at the joints and plump between the same joints, as seen in their fingers, arms, shoulders, which are thin, hollow, and long. But on the contrary, a man's joints are thick and knotty everywhere; and whereas children have hollow ones, men have raised ones. Leonardo da Vinci, Chapter 168.
* Between men and children, I find a great difference.