When someone asks about the 206 bones sitting around inside your body, the first ones that come to mind are probably the bigger ones. Maybe it’s the femur, the longest and strongest bone inside your body after all. It takes 4,000 newtons of force to break one, which is just under 900 pounds of force. But what about the bones that probably don’t get included in the skeleton model chilling inside your high school biology classroom? What is the smallest bone?
It’s All in Your Head
We promise we’re not trying to gaslight you. The smallest bone (in your body) is inside of your head. Specifically, your smallest bone sits inside of your ear. Inside of your ear are three bones that, together, form the ossicles–which is literally Latin for “small bone.” Bit of a misnomer, since the ossicles are made of three bones, but okay. Put together, the average person’s ossicles are no bigger than an orange seed.
Since everything comes in threes, your ear is divided into the external, middle, and inner ear. The ossicles sit in your middle ear along with your tympanic membrane (eardrum). This should tell you what the ossicles do. They connect your eardrum to your middle ear and vibrate with your eardrum to transmit sound into your head.
Since three bones make up the ossicles, we should probably name them. The three bones are called the malleus, incus, and stapes–Latin for hammer, anvil, and stirrup respectively. The average malleus is only 8 millimeters long and 2.7 millimeters wide. The incus comes in at 6.8 by 5.3 millimeters, but the stapes is even smaller. It’s just 3.5 millimeters long and 2.4 millimeters wide.
Specifically for the stapes, it acts like a tuning fork inside of your head. When sound goes into your head, the malleus strikes the incus, and the vibrations go through your stapes. The English names make a little more sense now, huh? Despite its size, damage to the stapes alone can give you some pretty bad hearing loss.
What’s the actual smallest bone?
Alright, you got us. If you read the title of the post you saw that we’re talking about the smallest bone–not the smallest bone you have.
The best place to start is probably by finding the smallest vertebrate. Meet paedophryne amauensis, a microhylid frog native to Papua New Guinea. These frogs are small enough to fit on a dime–only 7.7 millimeters from snout to butt. They’re a pretty new discovery too, first found in August 2009. They don’t even have a tadpole stage, they’re just born as smaller versions of themselves–as if they could get any smaller. Paedophryne amauensis also only has seven presacral vertebrae, which is fancy way of saying it has a reduced skeleton. Even their little frog hands and feet have less bones.
While we couldn’t find a paper where scientists took apart a paedophryne amauensis skeleton and picked out the smallest bone, we did find one where they measured some of their bones. For example, the width of the third finger disc on the average male frog of this species is between 0.15 and 0.25 millimeters. You can see the x-rays of paedophryne amauensis fingers, so at least we know the radius of the bones at the ends of their fingers.
You probably got like three, maybe four bones from this post, but can you get all 206 here?