Belly buttons. Everyone has one. Some are innies. Some are outies. And they always fascinate young children. Why humans have belly buttons and why some animals do--and others do no--is the subject of this informative, fascinating look at the lifeline that attaches mammals to their mothers before birth. Using simple but scientifically accurate terms and anatomically correct illustrations, the book carefully explains to children what umbilical cords are, how they help a developing fetus receive oxygen inside the mother's womb, and finally, how belly buttons (or navels) are created after the baby is born and the cord is cut. The book also depicts how humans and other mammals continue to nourish their young after birth, and looks at the special circumstances surrounding the births of certain animals, such as panda bears, African elephants, and blue whales.