Help with a foreach statement

I am writing a shopping cart.

Products assigned in the following fashion:
$_SESSION['selection'][$product]=$quantity;

I am wanting to display the list of products in the shopping cart in a
list for the user to see as they continue shopping.

I put the SESSION variable into $cart

$cart = $_SESSION['selection'];

then I start the foreach and this is where I get messed up.  I am trying
to ECHO the following syntax to the screen with each selected product:

The part I need help with is to write the foreach loop to give me
$product (so I may query the database to find out the product name) and
the $quantity (so I may show the user what they are purchasing).  The
part that is messing me up is that this is an array.

My ECHO statement should look like this:

echo "<li><a href=\"" . $path_to_shopping_cart . "product/" .
$cart[$product_id] . "/\">" . $product_name . "</a> - " . $quantity .
"</li>\r\n";