how to put bottom edge in an html row without css?

   <table>
   // aqui necesito que solo esto tenga un borde en al parte inferior
    <thead >
    <tr>
 <th>Producto</th>
 <th>cantidad</th>
 <th>Precio Unitario</th>
<th>Total</th>
</tr>
</thead>
   <tr>
  <td>ter</td>
 <td>10</td>
  <td>10</td>
  <td>19</td>
  </tr>
   <tr>
  <th></th>
 <th></th>
   <th>12</th>
  <th>12</th>
</table>