[MARCIANUS libro quinto institutionum. ] §38.16.9.prSi ex pluribus legitimis heredibus quidam omiserint adire hereditatem uel morte uel qua alia ratione impediti fuerint, quo minus adeant, reliquis, qui adierint, adcrescit illorum portio et licet decesserint, antequam adcresceret, hoc ius ad heredes eorum pertinet.
[MARCIANUS, from the fifth book of the Institutions.] If, out of several statutory heirs, some have neglected to enter upon the inheritance, or have been prevented by death or some other reason from entering, their portion accrues to the remaining heirs who have entered; and even if they have died before the accrual took place, this right belongs to their heirs.
alia causa est instituti heredis et coheredi substituti: huic enim uiuo defertur ex substitutione hereditas, non etiam, si decesserit, heredem eius sequitur.
The case is different for an appointed heir and one substituted for a co-heir; for to the latter, while alive, the inheritance is offered by virtue of the substitution, but if he has died, it does not also pass to his heir.