2 Children fully adopted, in accordance with the distinction drawn in our constitution, can bring this action as well as natural children, but neither can do so unless there is no other mode in which they can obtain the property of the deceased: for those who can obtain the inheritance wholly or in part by any other title are barred from attacking a will as unduteous. Afterborn children too can employ this remedy, if they can by no other means recover the inheritance. 3 That they may bring the action must be understood to mean, that they may bring it only if absolutely nothing has been left them by the testator in his will: a restriction introduced by our constitution out of respect for a father's natural rights. If, however, a part of the inheritance, however small, or even a single thing is left them, the will cannot be impeached, but the heir must, if necessary, make up what is given them to a fourth of what they would have taken had the testator died intestate, even though the will does not direct that this fourth is to be made up by the assessment of an honest and reliable man. 4 If a guardian accepts, under his own father's will, a legacy on behalf of the pupil under his charge, the father having left nothing to him personally, he is in no way debarred from impeaching his father's will as unduteous on his own account. 5 On the other hand, if he impeaches the will of his pupil's father on the pupil's behalf, because nothing has been left to the latter, and is defeated in the action, he does not lose a legacy given in the same will to himself personally. 6 Accordingly, that a person may be barred from the action impeaching the will, it is requisite that he should have a fourth of what he would have taken on intestacy, either as heir, legatee direct or fiduciary, donee in contemplation of death, by gift from the testator in his lifetime (though gift of this latter kind bars the action only if made under any of the circumstances mentioned in our constitution) or in any of the other modes stated in the imperial legislation. 7 In what we have said of the fourth we must be understood to mean that whether there be one person only, or more than one, who can impeach the will as unduteous, onefourth of the whole inheritance may be given them, to be divided among them all proportionately, that is to say, to each person a fourth of what he would have had if the testator had died intestate. TITLE XIX. OF THE KINDS AND DIFFERENCES BETWEEN HEIRS Heirs are of three kinds, that is to say, they are either necessary, family heirs and necessary, or external.