Checking delegation of zones

[Duncan Hill]

How does one check that a block has been delegated to one's 
nameserver?
  
In this case, 12.5.24.0 is listed on whois.arin.net as
being Penn College (where I work).  I have told the nameserver:
zone "24.5.12.in-addr.arpa" {
        type master;
        file "zone/12.5.24";
};

and the file itself looks like

$TTL 86400
24.5.12.in-addr.arpa.          IN     SOA
library.pct.edu. mwinder.pct.edu.
 (
                                        2000102701;serial
                                        10800   ;refresh
                                        3600    ;retry
                                        604800  ;expire
                                        86400 ) ;minimum

24.5.12.in-addr.arpa.          IN      NS      library.pct.edu.
254.24.5.12.in-addr.arpa.      IN      PTR     pat2.pct.edu.

(Yes, I know it isn't minumum any more.)

However, a lookup of 12.5.42.254 fails from anywhere but the server
itself.  How can I verify that the block has been delegated to our
server?

Thanks.

-- 

Sapere aude
My mind not only wanders, it sometimes leaves completely.