$(document).ready(function () {
  var elm = $('#subnavi > ul');
  elm.children("li").each(function() {
    var subelm = $(this);
    var ulelm = subelm.children("ul");
    if(ulelm.children("li").length == 1) {
       ulelm.children("li").attr('class', 'firstandlast');
    }
  });
});