[Iustiniani Institutiones]

q...to others, a nephew born from a natural and legitimate daughter is not in the power...
...it is not a maternal aunt to children born from my other natural and legitimate daughter. But what is the reason for the difference? I reply: because in the other case, namely when I adopt a grandson born from a daughter, it is in the same way a maternal aunt and uncle, because the elders, as they are present, command in...

And great. the same holds of up to above where it is said it cannot be estimated... A maternal aunt is the sister of a maternal grandmother; a great paternal aunt is the sister of a paternal grandfather, as in Digest on degrees and affinity, 3 and 4, par. "what of the paternal grandfather." I reply: it is a great paternal uncle, as in Code on the successor edict, law 1, 3. Observe what is noted there. But when they are in a narrow case, why are they prohibited, as in q. 5, par. "of the brother"? I reply: because these persons are from the upper ones transferred which are held in the place of parents as in this paragraph, and because she is in the first degree of the stem as noted above, par. "nor a grandson." And here it is not stated carefully: the order of transversals is divided into three parts, par. 1, 2, from the side, as in Digest on degrees, par. 2, in the 4th, 5th, and 6th, and the abstinence is greater toward the superiors, as here, than the inferiors, as above, par. "of the brother," and the transversals, as above, par. "of the two." Accursius Florentinus.

cannot be married

...that by reason of affinity marriages are impeded as here...

Item: if your stepdaughter
is still, that is, the daughter of her mother is
married to you, for that reason you cannot
take her as a wife
because it is not permitted to have
two wives at the same
time.
It is also prohibited to take
a mother-in-law and
a stepmother as a wife, because they are in the place of a mother, which also proceeds only when the affinity is dissolved; otherwise, if she is still your stepmother, that is, if she is still married to your father, it is impeded by every law for her to marry you, because the same woman cannot be married to two men.

Pa. says affinity...

Item: if she is still a mother-in-law, that is,
if her daughter is still
married to you, for that reason the marriage is impeded for you, because he cannot have two wives.
However, the son of a husband
from another wife and the
daughter of a wife from another husband, or vice versa,
can rightly contract a marriage

p Affinitas. Affinity is the regularity of persons separated by marriages, lacking all blood kinship, as in Digest on degrees, "not easily," par. "affines" and par. "it is to be known." Therefore, it says "from marriages" because without marriage it cannot be contracted. But according to the canons, it can even without marriage. But since a wife is seen to be an affine to the husband, why is it permitted to use the marriage? I reply: it is not the end of affinity.
q Of certain women. That is, stepdaughter. These names are explained immediately for the reader, in the words "that this means."
s Place. It makes for this, Digest on the solution of marriage, "because."
r Ought to be taken. Namely, this prohibition.
t Is married. That is, those who are contained by the name of these women, say as in Digest on this, law "adoptive," "let us see."

u Other reason. Not only the above-mentioned.
x Permitted. Rather, one is rendered infamous, as in Code on the Julian law of adultery.
y Mother-in-law. Who are these persons.
z Prohibited. By the law of affinity, from "a" to "b," which refers to "a" to "the thing itself."
a Law "him who."
b Says, as in Digest on this, "on the rites of marriage, law "adoptive," "now let us see."
d Says "z" on the office of the judge.

even though they may have
a brother or sister from a
marriage later contracted.
And if any
wife of yours after a divorce has procreated a daughter from another,
this woman is not indeed your stepdaughter, but Julian says
that one ought to abstain from marriages of this kind. For
it is established that neither the betrothed of a son
is a daughter-in-law, nor is the betrothed of a father
a stepmother; more rightly, however, those who have
abstained from marriages of this kind will be acting according to law.
This
is certain: that servile kinships also
are an impediment to marriage if perhaps a
father and daughter or brother and sister have been manumitted.
There are also other persons
who for diverse reasons are prohibited from contracting marriages, which in the
books of the Digest or Pandects from the old law...

c Affinity. This seems contrary to you; for if the affinity is dissolved, then the marriage is not prohibited by reason of affinity. I reply: it speaks of "dissolved," that is, when the marriage for which the affinity occurred is dissolved, but the affinity itself is not dissolved.
d Stepmother. Said here as if "harming the bow" or because she is a "new ark" without fruit.