A question about nested ajax loads.

A question about nested ajax loads.

Hi, I'm new to jQuery here, so I apologize if theres something obvious I'm missing.
 
I have a main page that loads "page1.php" into content div "content_div" via ajax load. 
 
However, I would like to add a button to "page1.php" that loads "page2.php" into "content_div", replacing the content of "page1.php".  How would I go writing the script that allows "page1.php" to use "content_div" in the main page?
 
Thanks