<li>
      <span style="position: absolute;bottom: 5px;width: 100%;text-align: center;">22222</span>
       <a class="img_b" href="#" Smallimg="images/2_s.jpg" Bigimg="images/2_b.jpg">
            <img alt="" width="150" height="150" src="images/2_s.jpg"/>
       </a>
 </li>

 $this.find("li").mouseover(function () {
     var myurl = $(this).find(''a'').attr("Bigimg"); //获取大图路径
     $(this).css("width",options.bigImgWidth).find(''img'').attr({src: myurl,width:options.bigImgWidth});
 });

  var  $lastLi；        
  $this.find("li").mouseover(function () {
      if ($lastLi != undefined) {
          var lasturl = $lastLi.find(''a'').attr("Smallimg");
          $lastLi.css("width",liwidth).find(''img'').attr({src: lasturl,width:liwidth});
      }
      var myurl = $(this).find(''a'').attr("Bigimg");
      $(this).css("width",options.bigImgWidth).find(''img'').attr({src: myurl,width:options.bigImgWidth});
      $lastLi = $(this);
 });

 var $getli = $this.find(''li'').eq(2);//这里又偷懒了，应该根据显示图片数量来判断中间图片
 var myurl = $getli.find(''a'').attr("Bigimg");
 $getli.css("width", options.bigImgWidth).find(''img'').attr({src: myurl, width: options.bigImgWidth});
 $lastLi = $getli;