Section 389. Any person interested may appear and defend

Any person
  interested in the property, or whose interests may be  affected  by  the
  final  order  or  judgment  of  registration  in the proceeding, whether
  specifically named in the notice or not, may  enter  his  appearance  by
  serving  a  copy of the same on the registrar of the county in which the
  property is located and with the clerk of  the  supreme  court  in  such
  county,  and  filing the original thereof together with proof of service
  with the county clerk on or before the return day or within such further
  time as may be allowed by the court; and may enter  his  objections,  if
  any,  by  likewise  serving  a  copy of the same on the registrar of the
  county in which the property is  located  and  with  the  clerk  of  the
  supreme  court  in such county, and filing the original thereof together
  with proof of service with the county clerk on or before the return  day
  or  within  such  further  time  as may be allowed by the court; and may
  oppose the petition for registration of the property as belonging to the
  petitioner, or set up a cross-demand to have the title registered in his
  own behalf. In any case, he shall state particularly what  his  interest
  is and shall specifically state all objections to the petition.