Alternative Method

gistfile1.txt

*** How to use
<?php echo open_ext("https://med.uth.edu/utms-universal/utms-superinclude-topnav.php"); ?>

*** What you include in your functions.php file
function open_ext($url){
$url = $url;
$content = wp_remote_fopen($url);
if ($content<>'') {
return $content;
} else {
echo 'Woops, I think something is going wrong!';
}
}