Setting Apart Every Firstborn Male to the Lord

"And you shall set apart" (Exodus 13:12)—"setting apart" means nothing but separation, and so it says, "And you shall pass on his inheritance to his daughter" (Numbers 27:8). Shimon ben Azzai says: "And you shall set apart every one that opens the womb"—what does this teach? Because it says, "All that pass under the rod" (Leviticus 27:32), I might understand that even the orphaned animal is included; and there is reason to argue so: if a blemished animal, which is unfit upon the altar, nonetheless enters the pen to be tithed, an orphaned animal, which is fit upon the altar, surely should enter the pen to be tithed. But a purchased animal, which is fit upon the altar yet does not enter the pen to be tithed, refutes this for the orphaned one. [The argument is balanced:] you cannot draw the orphan in by reasoning alone. It says "passing" here and "passing" elsewhere: just as the "passing" stated here means sanctity takes hold only during its mother's lifetime, so the "passing" stated elsewhere means sanctity takes hold only during its mother's lifetime. If here only males, perhaps elsewhere only males? Scripture teaches, "All that pass under the rod" (Leviticus 27:32)—both males and females are included. "And every firstling that comes of a beast" (Exodus 13:12)—a firstling "sent forth" by its mother. [If the firstborn miscarried,] it is exempt from the law of the firstborn, and the one that comes after it is not a firstborn. "Which you shall have" (Exodus 13:12)—to exclude one who sells the fetus of his animal to a gentile [the partial gentile share exempts it]. I might think to exclude one who sells his fetus to a gentile yet to include one who buys the fetus of a gentile's animal; Scripture teaches, "Whatever is born among your herd and your flock, the males" (Deuteronomy 15:19), to exclude one who buys the fetus of a gentile's animal. "The males shall be the LORD's" (Exodus 13:12). From here Rabbi Yose the Galilean used to say: a ewe that had not given birth before and bore two males, and the two heads emerged as one, both belong to the priest, as it says, "The males shall be the LORD's." But the sages say: it is impossible to be so exact; rather, one is his and one is the priest's.