trivial SSI doesn't work in apache2

I am running Debian Linux 3.1 on a Dell Dimension 4100 desktop. (This
host is 192.168.2.2 on my LAN.) I'm running apache2, and doing some
"finger exercises" to get better acquainted.

I created a trivial SSI and configured apache2 to serve it:

Document Root is /var/www in /etc/apache2/sites-enabled/000-default.

I added

<Location /ssi>
Options Includes
</Location>

and

<Location /ssi>
Options IncludesNoExec
</Location>

to /etc/apache2/sites-enabled/000-default.

I ran:

# a2enmod include
This module is already enabled!

and

# /etc/init.d/apache2 force-reload

I created /var/www/ssi, and in this directory I ran:

echo "top stuff" > top.html
echo "bottom stuff" > bottom.html

Then I created middle.shtml:

<!--#include virtual="top.html"-->
middle stuff!
<!--#include virtual="bottom.html"-->

Firefox serves my home page http://192.168.2.2 as expected.

When I point Firefox at http://192.168.2.2/middle.shtml
I expect to get the output:

top stuff
middle stuff!
bottom stuff

Instead, Firefox reports Error 404 ("Object not found!")

What am I missing here?

Thanks, as always, for your help.

Best Regards,

Vwaju
New York City