CLAVICULAR

Invented by primitive fish

On a slow Tuesday, clavicles

Are the first part of us

To start turning into bone

But the last to finish. They 

Are the only long bones

Which run horizontally. 

The name means "little key."

Instructions for making

Magic carpets, garters

And daggers may be read 

In a book called

"The Clavicle of Solomon."

Keys carved from clavicles

Are charms against lightning

But sometimes open doors

Better left firmly shut.