DIV里图片滚动显示？？

<div class="main">
  <div class="left"></div>
  <div class="center">
        <div class="item"><img src="5cm.JPG"></div>
<div class="item"><img src="b+ab.jpg"></div>
        <div class="down"><img src="00.JPG"></div>
  </div>
  <div class="right"></div>
</div>这是页面布局，问：如何让中间那三个div里的图片自下而上滚动？？？