Legacy of the thing which belongs only in part to the deceased or his successors

Where the testator, the heir or the legatee is the owner of only a part of the bequeathed thing or has only some right in such a thing, the bequest shall operate only to the extent of such part, or such right, except where it appears that the testator was convinced that the thing wholly belonged to him or to the heir or to the legatee; for, in this case, the provision of article 1801 shall be observed.