Mac Mail Preview Pane

My question is how do you set the Mail interface to show emails in your inbox and the contents of the email without actually "openning" the the email message?

I believe this is how it was set up when I first started using the program, but I recently noticed that my inbox just shows the list of emails without the option of the email preview pane.

Please let me know how to set this back up.

Macbook Mac OS X (10.4.7)

Macbook Mac OS X (10.4.7)

Macbook Mac OS X (10.4.7)