What I understand from the question is, you need this - http://www.php.net/manual/en/function.include.php
Create the menu in a separate PHP file and include that wherever you need the menu. Assuming your menu is in menu.php
In both includes/function-html.php
and stats.php
(assumption), wherever you need the menu, do something as follows.
<?php
...
//include menu here
include 'path/to/your/menu.php';
...
By doing this, you can customize menu.php
and it will reflect everywhere you have included it.
NOTE - Let me know in comments if that's not what you are looking for.