Chullin 4:2 - 4:3

מהבכרת המקשה לילד – with the first of her womb. It is permitted to cut it up limb by limb when it comes outfirst.

ומשליך לכלבים – for as long as its majority had not left [the womb], it is not holy.

יצא רובו – as one [complete animal], and [then] he cut it.

הרי זה יקבר – for with the exit of most, the sanctity takes effect upon it and we call it (Deuteronomy 15:19): “[You shall consecrate to the LORD your God all male firstlings] that are born [in your herd and in your flock.”

ונפטרה מן הבכורה – that which comes after him (i.e., the first-born male animal), is not a firstling, hether it first came out limb by limb, or whether the majority of it came out as one, for the second is not the first of the womb.

בבהמה טהורה טהור – from an a fortiori inference (see Tractate Hullin 70b), if [being inside] its mother is effective to permit it for consumption through its slaughter, even though it (i.e., the fetus) is dead, then should being inside its mother not also be effective to render it pure from the impurity of an animal carcass? And from where do we learn that the same applies regarding an unclean animal? For it states in Scripture (Leviticus 11:39): “If an animal that you may eat has died, anyone who touches its carcass shall be impure until evening.” [The phrase:” “If an animal…. has died,” this is an unclean animal; “that you may eat,” this is a clean–pure animal. A comparison of these juxtaposed “unclean animal” and “clean animal” – just as in a clean–pure animal, its fetus is pure, even in an unclean animal, its fetus is pure.

רבי יוסי הגלילי אומר בטמאה טמא – and he derives it from Scripture, as it is written (Leviticus 5:2): “Or when a person touches any impure thing -be it the carcass of an impure beast or the carcass of impure cattle,” Does the carcass of an impure beast defile and the carcass of a pure animal does not defile? But rather, which is it {that in an impure animal it defiles and that in a pure animal it doesn’t defile)? This is a [dead] fetus that is in the womb of an impure animal that is impure, and [a dead fetus] that is in a pure animal that is pure, from an a fortiori. But regarding the impure animal, there is no a fortiori [inference], and we don’t expound an analogy based upon biblical inference. But the Halakha is not according to Rabbi Yosi.

החיה טמאה טומאת שבעה – and it is from the Rabbis, as a decree lest the fetus bring forth its head outside the corridor–the lower end of the vagina or uterus, and he is like he was born and defiles and the midwife thinks that it (i.e., the fetus) is still in her womb and comes to be pure. But the shepherd who inserted his hand into the womb of the animal, as it is taught in our Mishnah is pure. We don’t make this decree, because the womb of the animal is revealed, and when it (i.e., the fetus) comes out, he sees it.

ואשה טהורה עד שיצא הולד – for the woman creates excitement for herself when it (i.e., the fetus) brings forth its head outside of the corridor–the lower end of the vagina or uterus, and he does not come to be purified (see Talmud Hullin 72a).