This is mysterious, isn't it? I have a 1.5-week-old kitten that I'm fostering for the local humane society and I haven't noticed any belly button on her or her two older foster brothers. But if I had seen these kittens when they were born, I would have seen the umbilical cord. Kittens in the womb get their nutrients from their mothers the same way we do, through an umbilical cord that's attached to the placenta on one end and the belly of the fetus on the other. All mammals have this system except for the marsupials (like kangaroos and opossums) and the two egg-laying mammals (platypus and echidna).

Blood from the mother carries oxygen and nutrients to the placenta and carries wastes away. The cleaned, fueled, oxygen-rich blood then flows through the fetus. So why are we the only mammals (as far as I know) with visible belly buttons? Basically, the answer is that the belly button heals more completely in kittens than in us, butwhy? Maybe it's because of how we tie off and cut the umbilical cords of babies. Most mammal mothers bite the cord between the baby and the placenta, leaving a fairly long piece of the cord. Then the cord shrivels up over the next few days and falls off. I wonder if we'd have belly buttons if we did the same thing. Maybe it's because our skin is rather different than the thin skin of most mammals. Now I'm wondering if chimps have visible belly buttons.

What a great question! It never occurred to me that cats should have belly buttons. You see the attached bit of umbilical chord on newly-born puppies, so puppies must have them, but what about cats? Basically, all mammals that develop in a placenta, attached to their mother with an umbilical chord, should have a belly button or at least a scar where the umbilical chord attached. (There IS a group of mammals that do not develop in placentas, and thus do not have belly buttons. Can you think of an example? You won't find them in North America!) According to Cecil Adams, the guy who answers questions for "The Straight Dope" column ( straightdope ), cats have a scar hidden under their fur just tail-wards of their rib cage where the umbilical chord attached. This is the cat equivalent of a belly button.

Cats do have umbilical cords (which is how they get nutrients), and normally the mother cat severs it with her teeth, and the belly button will not appear as humans do - the mother cat does not tie a neat knot!!!