赤ちゃんの骨の数が大人より多い理由は？約300本が206本に

Why Do Babies Have More Bones Than Adults?

Today is Halloween, and many houses have a plastic skeleton outside.

A real adult skeleton has 206 bones.

A baby is born with about 300 bones.

So how can a baby have more bones than you?

The answer is that many of a baby's bones are not finished yet.

Some parts of a baby's skeleton are made partly or fully of cartilage.

Cartilage is soft and flexible.

During childhood, the cartilage is slowly replaced by hard bone.

As a child grows, some small bones grow together and become one big bone.

This is why the number goes down.

The skull is a good example.

A baby's skull has soft gaps between its bones.

These gaps let the head change shape a little when the baby is born.

They also give the brain room to grow, because the brain grows faster than the bone around it.

The gaps close slowly, and most are closed by the time a child is one and a half.

By the age of about 25, almost all of your bones are completely hard.

Bones are not dead. They are alive.

Inside many bones, there is a soft, jelly-like part called marrow, and it makes blood cells.

So when you see a Halloween skeleton tonight, remember this.

A real skeleton is alive, and it has changed a lot since you were a baby.