How to work around FORM method="post" changing "." to "_" please?

here is my form:

<html>
<head></head>
<body>

<FORM ACTION="code.php" method="post">
<INPUT TYPE=SUBMIT NAME="arty.jpg" VALUE="Action">
</FORM>

</body>
</html>

here is code.php:

<?php
if(!empty($_POST)){
foreach($_POST as $myFile => $value){
echo "$myFile";
}
}
?>

What I was expecting is that the code would print out "arty.jpg" when
you click the button.

Instead it prints out "arty_jpg"

So the Post method is changing "." to "_"

But I need to pass the filename which may include both "_" and "."
character.

I guess I need some kind of escape and unescape funtion.

Please can someone reccomend one.

PS I am working on a file upload / downalod / delete form at this
link:

http://willyhoops.com/upload/

Many Thanks...

.