Can’t Modify Comments?

Hello. I am customizing comments for my blog and have customized the comments.php file. However, I’m having a problem finding the template that is used to create each individual comment. It looks like word press just wants me to let…

<?php wp_list_comments(); ?>

handle everything with only being able to change certain style features by passing them in as arguments. I want more than this. I want to add my own code inside each comment and add separators between comments (but not at the end), and I want to change the layout of each individual comment.

I’m sure people have done this before but I’ve searched and can not find any help on this. If someone could help me out here it would be much appreciated. Thank you.