A puzzling Tosafot about C-sections: Can a baby be born rectally?

Ishim veShittot tells of an interesting anatomical discussion in Tosafot in Keritut 7b.

The Mishna there relates:

מתני' יש מביאות קרבן ונאכל ויש מביאות קרבן ואינו נאכל ויש שאינם מביאות [מביאות] קרבן ונאכל המפלת כמין בהמה חיה ועוף דר"מ וחכ"א עד שיהא בו מצורת אדם המפלת סנדל או שיליא או שפיר מרוקם והיוצא מחותך וכן שפחה שהפילה מביאה קרבן ונאכל ואלו מביאות ואינן נאכלות המפלת ואין יודע מה הפילה ושתי נשים שהפילו אחת ממין פטור ואחת ממין חובה א"ר יוסי אימתי בזמן שהלכו זה למזרח וזה למערב אבל אם היו שתיהן עומדות שתיהן מביאות קרבן ונאכל אלו שאין מביאות המפלת שפיר מלא מים מלא דם מלא גנינים המפלת כמין דגים וחגבים ושקצים ורמשים המפלת יום ארבעים ויוצא דופן ר' שמעון מחייב ביוצא דופן:

The discussion is whether there is an obligation to bring the korban of a yoledes, and there is a dispute regarding the Tanna Kamma and Rabbi Shimon.

Surprisingly, Tosafot do NOT define yotzei dofen as a Cesarean section, cutting open the mother's belly and extracting the baby. They rather propose and discuss two other possibilities. another possibility (See update). Why should this be?

I would suggest that it is because of the same thing Rambam discusses in his perush haMishnayos on Bechoros, in the eighth perek. There, we read the Mishna and Rambam's comment (see this parshablog post):

Mishnah: A child born via Cesarean section, and the one who comes after him, neither of them is the firstborn, not to inheritance nor to the kohen. Rabbi Shimon says: The first one to inheritance and the second one to the five selaim {to redeem him from the kohen}.

Rambam: What is possible to be in this is that the woman was pregnant with two fetuses, and her belly was ripped open and one of them came out, and subsequently the second one came out in the normal way {, that is, vaginally}. But that which some relate, that the woman lives after they rip open her belly, and she becomes pregnant and then gives birth, I do not know of any grounds for it, and it is a very strange matter. And the halacha is not like Rabbi Shimon.

Thus, it is clear that the woman survives the C-section, but in medieval times a woman did not survive a C-section. Nowadays, of course, women (once again?) survive them.

So it is possible that the Baalei HaTosafot were well-aware of this process of removing an infant from its mother via C-section, after her death, or causing her death, but did not consider it a possible meaning of yitzei dofen because the Mishna makes it clear that the mother survives. Or it is possible that they were unaware since the procedure had fallen out of practice because of its fatal effect on the mother.

At any rate, Tosafot write as follows, on the daf in Krisus:

יוצא דופן. פי' ע"י סם פתחו לכריסה והוציאו הולד. ור"י לוי פי' דיצא דרך בית הרעי ואין נראה מדקאמר בפ"ק דבכורות גבי דג טמא שבלע דג טהור כגון שנמצא דרך בית הרעי ש"מ שא"א לצאת דרך בית הרעי אא"כ בלע שנכנס דרך הוושט אבל מה שמשריץ בתוך מיעיו לא יצא דרך בית הרעי:

Roughly:
Leaves via the wall: To explain, via an drug acid [thanks, to Wolf2191; see comments] they open her belly and take out the child. And Ri Levi explains that it went out via the rectum. And this does not appear so, from the fact that we state in the first perek of Bechorot regarding a non-kosher fish which swallowed a kosher fish, such that it is found by the end of the digestive tract, by the rectum. We derive from this that it is impossible for it to exit via the digestive tract unless it entered via the throat, but that which became a sheretz within its belly does not go out via the tract leading to the rectum.

This is indeed strange. I am not sure how to translate ע"י סם פתחו לכריסה והוציאו הולד. This does not seem to be inducing natural labor, for they refer to kreisah rather than rachmah. And they make no mention of a scalpel for cutting open her belly, only a sam, a drug. This would be C-section via drug, which is strange. Update: via an acid.

The second suggestion, of Ri Levi, is stranger. I don't think it is indeed possible. Naturally, the method of disproving it is not via appeals to medical experts of the day, but proofs from a Talmudic text. But who says that fish anatomy is the same as human anatomy?! Indeed, birds lay eggs out of their rectum, as the vagina and rectum combine into the cloaca.