But also imagine if they were filled with solid bone -- our head would be dead weight, we wouldn't be able to hold it erect, we wouldn't be able to look at the world around us.
Agora imaginem, se fossem ossos sólidos, nossa cabeça seria tão pesada que não conseguiríamos mantê-la erguida, não seríamos capazes de olhar o mundo ao nosso redor.