Loopy Post Navigation

Make posts loop back around to the other end:

<?php
function apple_post_navigation()
{
	global $post;

		$categories = get_the_category( $post->ID );
		$category = $categories[0]->cat_name;
		$last_post = get_boundary_post( TRUE, '', FALSE );
		$first_post = get_boundary_post( TRUE, '', TRUE );
		?>
    <div class="prev_next">
        <div class="nav_left">
            <span class="prev">
            <?php 
            if(get_adjacent_post(TRUE, NULL, TRUE)){
				previous_post_link('%link', '< Previous '.$category , TRUE);
			} else {
				print $last_post->ID;
				print '<a rel="last" href="'.get_permalink($last_post[0]->ID).'">< Previous '.$category.'</a>';
			}
			 ?>
            </span>
         </div><div class="nav_right">
            <span class="next">
            <?php 
            if(get_adjacent_post(TRUE, NULL, FALSE)){
				next_post_link('%link', 'Next '.$category.' >' , TRUE);
			} else {
				print $first_post->ID;
				print '<a rel="first" href="'.get_permalink($first_post[0]->ID).'">Next '.$category.' ></a>';			
			}
			 ?>
			 </span>
        </div>
    </div>
<?php

}
?>