against the tenant, if he is of full age and prepared to prove his age, the tenant will  not be heard if he wishes to vouch the chief lord to warranty because of some agreement  made between them, as where he says that he is bound to warrant him up to a  certain term, or beyond the full age of the heir, since that agreement does not touch  the heir. Let the assise proceed immediately, and let the tenant sue on the agreement  against his warrantor, if he thinks it expedient, because the demandant by the assise  of mortdancestor claims nothing in the wardship, nor is the vendor bound to warrant  anything to the tenant except the wardship, not the tenement in demesne.
Of the exceptions to be put forward against an assise of mortdancestor.
 When [the tenant] in the assise of mortdancestor has no warrantor, or though he has  vouches none, because he prefers to undertake the defence himself, many answers and  exceptions are available to him arising out of the clauses of the writ, and let him first  put those forward. The first thing said is if such a one, the father (or mother) etc.,  and thus we must first see on whose death the assise ought to be taken.1
On whose death the assise ought to be taken.
 It is clear that it is on the death of a father or mother, a brother or sister, an uncle or  aunt. And as it is limited to certain persons, so is it limited within certain degrees,  so that it does not extend upward to a grandfather nor downward to a grandson,  because the assise will never lie on the death of a grandfather, nor similarly on the  death of a nephew, though the nephew may have the assise on the death of an uncle  or aunt. Nor will the assise ever lie between kinsmen, brothers and sisters, grandsons  and granddaughters, greatgrandsons and greatgranddaughters, and so on  descending, [nor will cosinage,] with respect to any inheritance or for anything which  descends hereditarily from a common stock, only the writ of right; but against  strangers the assise will lie in so far as it extends. For those persons to whom the assise  does not extend, cosinage lies, which derives entirely from the assise, as will appear  more fully below.2
How the demandant ought to prove his claim.
 Once the demandant has put forward his intentio he must support and prove, by  the assise in the manner of an assise, all the clauses of the writ, that is, that such a  one, the ancestor whose seisin he claims, was seised, and in his demesne as of fee,  and on the day he died, and that he died after the term, since this assise like the  others is limited to a certain term. And if he fails as to one of these clauses the assise  will fall as though he had failed in all.