$(document).ready(function(){
    $("#top_nav ul li").hover(
      function () {
        $(this).children("ul").css("display","block");
      },
      function () {
        $(this).children("ul").css("display","none");
      }
    );
});

$(document).ready(function(){
    $("#top_menu ul li").hover(
      function () {
        $(this).children("ul").css("display","block");
      },
      function () {
        $(this).children("ul").css("display","none");
      }
    );
});