The first commentary on birds, for this codex, are made on the second page of the fourth folio. Leonardo describes how the tips of a bird's feathers are always the highest part of the bird, when its wings are lowered, and how the bones in the wing are the highest part of a bird when its wings are raised. He writes on the heaviest part of a body being the location that guides movement for that body. He also questions what part of the wing of a bird experiences the greatest amount of air pressure. To end this folio, Leonardo states how an object, "that does not bend under the pressure of objects of different sizes and weights", will distribute its weight to its supporting points that surround the center of the object.