This is why it is so carefully guarded from injury.
~6.

The Backbone.~--The framework of the back is called the _backbone_.
This is not a single bone, but a row of bones arranged one above another.

Each bone has a hole through it, about as large as one of your fingers.

A large branch from the brain, called the _spinal cord_, runs down through the middle of the backbone, so that the separate bones look as if they were strung on the spinal cord, like beads on a string.
~7.

The Trunk.~--The trunk of the body, like the skull, is hollow.