How do I strip Name and Email Address requirements from a php 'send comment' form?

My pre-apologies for not being well-versed in php, but I am trying to put together a simple Comment box for users to "drop me a line".  I know this might seem strange, but for this particular purpose I don't want to require a Name and Email Address form field. How do I remove it from the following simple php so that the feedback comes through to my email?

Must be an easy thing, right?

Thanks,

Dave

<?php
/*
This first bit sets the email address that you want the form to be submitted to.
You will need to change this value to a valid email address that you can access.
*/
$webmaster_email = "example@example.com";

/*
This bit sets the URLs of the supporting pages.
If you change the names of any of the pages, you will need to change the values here.
*/
$feedback_page = "feedback_form.html";
$error_page = "error_message.html";
$thankyou_page = "thank_you.html";

/*
This next bit loads the form field data into variables.
If you add a form field, you will need to add it here.
*/
$email_address = $_REQUEST['email_address'] ;
$comments = $_REQUEST['comments'] ;
$first_name = $_REQUEST['first_name'] ;
$msg =
"First Name: " . $first_name . "\r\n" .
"Email: " . $email_address . "\r\n" .
"Comments: " . $comments ;

/*
The following function checks for email injection.
Specifically, it checks for carriage returns - typically used by spammers to inject a CC list.
*/
function isInjected($str) {
$injections = array('(\n+)',
'(\r+)',
'(\t+)',
'(%0A+)',
'(%0D+)',
'(%08+)',
'(%09+)'
);
$inject = join('|', $injections);
$inject = "/$inject/i";
if(preg_match($inject,$str)) {
return true;
}
else {
return false;
}
}

// If the user tries to access this script directly, redirect them to the feedback form,
if (!isset($_REQUEST['email_address'])) {
header( "Location: $feedback_page" );
}

// If the form fields are empty, redirect to the error page.
elseif (empty($first_name) || empty($email_address)) {
header( "Location: $error_page" );
}

/*
If email injection is detected, redirect to the error page.
If you add a form field, you should add it here.
*/
elseif ( isInjected($email_address) || isInjected($first_name) || isInjected($comments) ) {
header( "Location: $error_page" );
}

// If we passed all previous tests, send the email then redirect to the thank you page.
else {

mail( "$webmaster_email", "Feedback Form Results", $msg );

header( "Location: $thankyou_page" );
}
?>