The end of your backbone
Your backbone ends with two special bones. Each one is made of smaller bones joined together. First comes the sacrum. Then, at the very tip, comes the tailbone.
The sacrum is a big triangle of bone at the back of your hips. It starts as 5 vertebrae, the small bones of the backbone. They slowly join into one bone during the teen years.
The tailbone is tiny. It's made of 3 to 5 little vertebrae, most often 4, joined together.
Its science name, coccyx, comes from the Greek word for cuckoo. People long ago thought it looked like a cuckoo bird's beak.
A leftover from long ago
Lots of animals, like monkeys, cats and dogs, have tails. Long, long ago, the animals that humans came from had tails too.
Over a very long time, the tail got smaller and smaller. Today, all that's left is your little tailbone, tucked inside.
Chimpanzees and gorillas don't have tails either. They have tailbones, just like you!
Its jobs today
Your tailbone isn't useless. Muscles and strong straps called ligaments hold on to it. Some of them help hold up the soft parts inside your belly, like a hammock.
Part of your big bottom muscle, the glutes, holds on near it too.
When you sit and lean back, some of your weight rests on your tailbone. It works with your two sitting bones, a bit like the three legs of a stool.
Ouch, I landed on it!
If you slip and land hard on your bottom, your tailbone can get bruised. It can feel sore to sit for a while.
The good news is that a bruised tailbone gets better with time, often in a few weeks. Sitting on a soft cushion can help it feel better while it heals.