How can I select all divs appearing below a given div in jquery?

Question

I want to use slideToggle and ensure everything below the selected div is push down without affecting the rest of the page.. I tried adding a class label 'underneath' to each div beneath the selected one but this really isn't scalable..

I've adapted this tutorial for the dropdown: http://www.derby-web-design-agency.co.uk/blog-post/how-to-create-a-jquery-slidedown-toggle-effect-div-tutorial/22/

This is my js function, called when a button is clicked:

if($(".dropdownwrap:visible").length > 0)
{        
    $(".dropdownwrap").slideToggle("slow");
    $(".underneath").stop().animate({"margin-top":"0px"}, "slow");
}
else
{
    var size = parseInt($('#'+id).css("height"));
    size = size + 120;        
    $(".underneath").stop().animate({"margin-top": size + "px"}, "slow");        
    $(".dropdownwrap").slideToggle("slow");
}