In calculating the degree of consanguinity special attention must be paid to three things, the line, the degree, and the stock or root. The
stock, or root, is the common ancestor, or the
person, male or
female, from whom descend as from the nearest common bond the
persons whose blood-relationship is to be determined. The
degree is the distance of one
person from the other in regard to blood-relationship. The
line is the classified series of
persons descending from the common stock through one or more generations. The line is direct when the series of
persons descend one from the other, as father and son, grandfather and grandchild. The line is transverse, or
collateral, when the blood-relations spring from a common stock, yet do not descend one from the other but form different branches side by side, as two brothers, two nephews. This collateral line is equal or unequal according as these
persons derive equally or unequally from the same stock or root. The blood-relationship is computed according to the distance from the stock whence it is derived, and this is the rule by which the degrees or steps of consanguinity are determined.
…
…But the Canon law, in the collateral line of consanguinity, computes for marriage one series only of generations, and if the series are unequal, only the longer one. Hence the principle of canon law that in the transverse or collateral line there are as many degrees of consanguinity as there are
persons in the longer series, omitting the common stock or root. If the two series are equal, the distance is the number of degrees of either from the common stock. Thus brother and sister are in the first degree, first cousins in the second degree; uncle and niece in the second degree because the niece is two degrees from the grandfather who is the common stock. Thus if Caius has two sons, Titius and Sempronius, and Sempronius has a son and grandchild, the relationship of the grandchild of Sempronius to Titius is in the third degree, because this grandchild is distant three degrees from the common stock, Caius…