That's what we like to call, the "navbar" - Navigation Bar.
When it is generated automatically, the makenavbar() function is used.
That function can be found in the functions.php file.
I'm telling you now, it is only used on about 7, maybe 8 of the pages.
These are showthread, newreply, newthread, forumdisplay, editpost, and a couple more I can't remember right now.
For the other pages, it is just written in the templates (e.g usercp, modifyprofile, modifyoptions, etc).
Where it is generated by the function, this is how it'll be called:
PHP Code:
$navbar=makenavbar(couple,of,arguments,here);
In newreply.php it's:
PHP Code:
// draw nav bar
$navbar=makenavbar($threadid,"thread",1);
and the same in newthread.php, only with $forumid and "forum".