wp_nav_menu () reverse order

I don’t know how, but why is wordpress showing my menu in reverse order ?

functions.php

// Menu Support aktivieren
add_action( 'init', 'register_my_menus' );
function register_my_menus() {
register_nav_menus(
array(
'primary-menu' => __( 'Primary Menu' ),
'secondary-menu' => __( 'Secondary Menu' ),
'tertiary-menu' => __( 'Tertiary Menu' )
)
);
}

header.php
<?php wp_nav_menu( array('menu' => 'Primary Menu', 'sort_column' => 'menu_order', 'container_class' => 'menu-header')); ?>

Please help