Jak dodać<thead> i<tbody> to za pomocą jquery?

problem jest taki, że moja tabela ma 1 lub 2 wiersze?

$('#myTable tr:has(th)').wrap('<thead></thead>');

<table id="myTable">

<tr><th>1</th><th>2</th><th>3</th><th>4</th></tr>
<tr><th>1</th><th>2</th><th>3</th><th>4</th></tr>

<tr><td>1</td><td>2</td><td>3</td><td>4</td></tr>
<tr><td>1</td><td>2</td><td>3</td><td>4</td></tr>
<tr><td>1</td><td>2</td><td>3</td><td>4</td></tr>
<tr><td>1</td><td>2</td><td>3</td><td>4</td></tr>
<tr><td>1</td><td>2</td><td>3</td><td>4</td></tr>



</table>