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@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