Gemara

Questions (Rava): Is the child Kodesh if it left the womb wrapped (through people) in tendrils (vine sprigs)? If it left in a garment, what is the law? If it left in its fetal sac, what is the law?

Objection: It is normal to leave in its fetal sac. Clearly this does not inhibit the Kedushah!

Correction: Rather, it was wrapped in a fetal sac of another fetus.

Question: If she covered it when it came out, is it Kodesh

Question: If the head left first, this is obvious!

Answer: Rather, the feet left first.

These questions are not resolved.

70b (Mishnah): If a shepherd touched a dead fetus inside an animal, his hand is Tahor, whether the animal is Tahor or Tamei.

Bechoros 9b -Suggestion: (Chachamim say that Iy Efshar Letzamtzem, i.e. it is impossible for things to happen simultaneously. Therefore, if it seems that two males came out together, one of them is a Bechor.) Chachamim must hold that even part of the (circumference of the) womb is Mekadesh (a Bechor);

If all of the womb were needed to be Mekadesh, even though Chachamim say that Iy Efshar Letzamtzem, if twins left almost at the same time, the second was a Chatzitzah (separation) between the Bechor and the womb!

Rejection (Rav): (Perhaps all of the womb is Mekadesh.) The second animal is the same species. Min b'Mino is never Chotzetz.

Rishonim

Rambam (Hilchos Bechoros 4:17): If a Bechor was wrapped in tendrils and left the womb without touching it, or it was wrapped in the fetal sac of another fetus, or its sister was wrapped around it, since it did not touch the womb, it is a Safek Bechor.

Rashi (70a DH Mahu): When it was wrapped, do we say that it is a Chatzitzah, and since it did not touch the walls of the womb, it is not Kodesh? The womb is Mekadesh, and the Torah said that Kedushah depends on it. The Gemara asked about a fetal sac, for even if tendrils are a Chatzitzah, perhaps this is because it is Eino Mino (not the same substance as the fetus). A fetal sac is Mino.

Rashi (70a DH Karchah): We asked about if a woman held it in her hands and took it out. Her hands separate between it and the womb. Do we say that since it is normal to do so, it is not a Chatzitzah?

Rashi (70a DH Iy): If the head left first, obviously it became Kodesh! Once the head left, it is born. Rather, the feet left first, and it was wrapped before the majority left.

Tosfos (70a DH Karachto): The Gemara never discusses a woman helping an animal gave birth. It always discusses a shepherd. Also the first questions are in the masculine (if he wrapped it in tendrils...) Also, why is it obvious (that it is a Bechor) if the head left first? Perhaps she held his head before it left the womb! It is difficult to say that the womb does not open and she cannot put her hands in before the head comes out. Our Mishnah (70b) discusses a shepherd who entered his hand before anything came out. If not, he became Tamei through what left! One could say that a first birth is different, or the Mishnah discusses twins and he entered his hand after one fetus already left, but this is difficult. Rather, the text here is like R. Chananel says, 'his sister wrapped him.' A female was born with the male. If the male (i.e. and also the female) left head first, her head surely left first, for his head was wrapped in her legs! Rather, the legs left first. We could have said that the head was wrapped in a male twin, and we ask which is the Bechor. We asked about a case in which (perhaps) there is no Bechor at all.

Ramban (70a DH Girsas): R. Chananel's text says that he was surrounded by a female twin. Rava could have asked which child is Kodesh when twin males are born and one covered the other (the first head to leave was covered).

Tosfos (9a DH Amar): Here, Rav says that Min b'Mino is not a Chatzitzah. In Chulin, we asked whether a female twin is a Chatzitzah! We can say that here, part (of the womb) is free, so there is more reason to say that Min b'Mino is not a Chatzitzah. (Tzon Kodoshim - since they came out together, one did not totally wrap the other. There, the female totally covered the male.) Alternatively, another male is Mino more than a female. We could also say that there, the female helped the male leave. If not, surely it is not a Chatzitzah.

R. Gershom (9b DH d'Iy): The Gemara asked that if the entire womb is Mekadesh, i.e. all sides, why do Chachamim say that one of them is Kodesh? Neither head touched the womb on all sides!

Poskim

Tur (YD 315): If a Bechor was wrapped in tendrils, or in the fetal sac of another fetus, or its sister was wrapped around it, since it did not touch the womb, it is a Safek Bechor.

Chelkas Yo'av (cited in Avnei Nezer YD 392:7): Regarding Bechor, even a minority Chatzitzah disqualifies. The Gemara said that even if Iy Efshar Letzamtzem, one is a Chatzitzah. It is known that everything has four directions. When twins leave together, each touches the other only on one side. For each of them, the majority of the circumference of the head touches the womb.

Note: It would be possible for the head of each fetus to be mostly wrapped in the legs of the other. However, they would have to be miniscule in order to leave the womb in this position in such a way that it looks like both heads left at once. Further, this is a very remote possibility. Since the Mishnah did not specify that this is the case, the Gemara could not assume so in order to deduce that even part of the womb is Mekadesh.

Chelkas Yo'av: Do not say that it is because the womb itself has a Chatzitzah. (I.e. we do not require that the fetus touch the womb, rather, the womb must touch the fetus. If we would say the latter way, Chatzitzah would depend on covering the majority of the womb - PF.) The Gemara in Chulin asked only about when most of the walls of the womb had fallen, and the fetus left through an area where they were intact. If half the wall was intact (and it left through there), surely it is a Bechor. This shows that the Pesul is only because it touches another fetus. Even a Chatzitzah on the minority disqualifies, unlike Tevilah.

Avnei Nezer (393:12): Indeed, it is because the womb itself has a Chatzitzah! Only the entire womb is Mekadesh.

Avnei Nezer (394:1,2): The problem of Chatzitzah is not that the fetus did not touch the entire womb, rather, that the entire womb did not touch the fetus. Even if the minority of the womb touched the entire fetus, it would not be Kodesh. R. Gershom explains that it is because the womb did not touch all around the fetus, even though he holds that a tradition from Moshe from Sinai teaches that a minority is not a Chatzitzah. If not for the tradition, it would be a Chatzitzah. Tosfos Yeshanim (Eruvin 4b) says that if not for the tradition, one might have thought only a total Chatzitzah disqualifies. Yevamos 78a-b connotes like this. It says that a minority is not a Chatzitzah when he is not particular about it, but a total Chatzitzah is a Chatzitzah. I.e. the tradition is only about one who is concerned. If he is not concerned, only a total Chatzitzah disqualifies. If so, we should say that for a Bechor, only a total Chatzitzah disqualifies. Even if we compare it to Tevilah, the minority is not a Chatzitzah. Rather, we must say that the problem is that the entire womb must be Mekadesh.

Ateres Paz (1:2:17:2): Perhaps the Safek is only when the Chazakah is on the entire fetus or its majority. Regarding Tevilah, only a majority that one is adamant about is a Chatzitzah mid'Oraisa. The Rishonim say similarly about a Chatzitzah between a Kohen's feet and the floor of the Azarah. Chelkas Yo'av (26) says that for Bechorah, even a minority is a Chatzitzah, and R. Gershom clearly says so.

Igros Moshe (YD 3:125 DH u'Mah): The Avnei Nezer connotes that Rava holds that perhaps Chatzitzah does not apply to Bechor at all. It is astounding to say that he argues with the Stam Gemara in Bechoros, to which it was obvious that Chatzitzah applies. Rav or Rav Ashi agrees that Chatzitzah applies, just he holds that Min b'Mino is not a Chatzitzah. Tosfos and the Ramban did not discuss this at all. If Tosfos held that Rava argued with the Sugya, he would have asked this. There is no answer for it! Even though the Ramban said that they argue, he means that Rava holds that even Min b'Mino can be a Chatzitzah. He did not say that Rava has a Safek whether Chatzitzah applies. Rava asked about tendrils, for it is for the sake of the fetus. It was a cold, day, and the shepherd wrapped it to spare it pain. The Gemara asked separately about a garment, since perhaps tendrils are a Chatzitzah because it does not warm so much, so it is not considered for the sake of the child. A garment warms as much as needed, so perhaps it is not a Chatzitzah. We asked about a fetal sac, for it is normal and it helps the fetus, and (perhaps) it is Min b'Mino. Rashi says that the next question was about a woman helping deliver. He did not explain that we ask about a twin, for in Bechoros Rav (some texts - Ashi) says that Min b'Mino is not a Chatzitzah. Tosfos says that we ask about a twin sister, and he distinguishes between males and females, or between partial and total Chatzitzos. The Ramban does not distinguish. He holds that Rava argues with Rav Ashi.

Ateres Paz (ibid.): Perhaps the Safek is only when the Chazakah is on the entire fetus or its majority. Regarding Tevilah, only a majority that one is Makpid (adamant) about is a Chatzitzah mid'Oraisa. The Rishonim say similarly about a Chatzitzah between a Kohen's feet and the floor of the Azarah. Chelkas Yo'av (26) says that for Bechorah, even a minority is a Chatzitzah, and R. Gershom clearly says so.