When a person, not a party to the proceedings, claims a share assigned to or left for a part owner, he is concluded so far as it respects the assignment of the share, but he is not prevented from maintaining an action within the time in which it might have been brought if no judgment for partition had been rendered, for the share claimed, against the tenant in possession, the same as if the plaintiff had claimed the piece demanded, instead of an undivided part of the whole.