Jquery change select option next previous buttons AND Load c


<!DOCTYPE html>
<html>
<head>
  <script type='text/javascript' src='http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js'></script>

  <style type='text/css'>
  .block{
  background: #333333;
  color: #fcfcfc;
  width: 800px;
  padding: 5px;
  margin:5px 0px 0px 0px;
  border: 2px #fff;
  }
  </style>

<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
$(document).ready(function () {
    $('.block').hide();
    $('#option1').show();
    $('#selectField').change(function () {
        $('.block').hide();
        $('#'+$(this).val()).fadeIn();
    });
});
});//]]>

</script>
</head>
<body>
<center>
<button type="button" id="prev">Previous</button>
<select id="selectField" style="padding-left: 20px;width:150px">
        <option value="option1">Lion</option>
        <option value="option2">DOG </option>
        <option value="option3">Cat</option>
        <option value="option4">Lion</option>
    </select>
<button type="button" id="next">Next</button>

 <div id="option1" class="block"></div>
 <div id="option2" class="block">DOG </div>
 <div id="option3" class="block">Cat </div>
 <div id="option4" class="block">Mouse</div>

 </center>
</body>
</html>