pg_class.relfilenode for large tables

Hi all,
when a table becomes large a new file on disk is created. Such file has the
name compound by the pg_class.relfilenode attribute and an incremental index.
However it seems to me this does not appears in the pg_class table. Is there
any place where this extra file appears?

As an example:

postgres(at)fluca:~$ ls -l /opt/database/24601/41098* -h
-rw------- 1 postgres postgres 1,0G 2007-08-20 08:48 /opt/database/24601/41098
-rw------- 1 postgres postgres 202M 2007-08-20
08:49 /opt/database/24601/41098.1

select oid, * from pg_class where relname='large';

oid | relname | relnamespace | reltype | relowner | relam | relfilenode |
reltablespace | relpages | reltuples | reltoastrelid | reltoastidxid |
relhasindex | relisshared | relkind | relnatts | relchecks | reltriggers |
relukeys | relfkeys | relrefs | relhasoids | relhaspkey | relhasrules |
relhassubclass | relfrozenxid | relacl | reloptions
-------+---------+--------------+---------+----------+-------+-------------+---------------+----------+-------------+---------------+---------------+-------------+-------------+---------+----------+-----------+-------------+----------+----------+---------+------------+------------+-------------+----------------+--------------+--------+------------
41098 | large | 2200 | 41099 | 16386 | 0 | 41098 |
0 | 156813 | 1.12921e+07 | 0 | 0 | f |
f | r | 9 | 0 | 0 | 0 |
0 | 0 | f | f | f | f |
11412913 | |
(1 riga)

Thanks,
Luca