The laws concerning a limb extended from the womb of a pregnant animal (אבר היוצא) and a mauled limb (אבר המדולדל)  hanging from the body of an injured animal and the laws concerning a live fetus borne after shehitah (בן פקועה) has been performed on its mother are explained in seventh chapter of the tractate, “Beheimah Ha-Meqasheh.” The understanding of the relevant sugyot is subject to great controversy among the Talmudic commentators and the halakhic authorities.

In Hilkhot Ma’akhlot Assurot (5:9) the Rambam writes:

 If a fetus extends its foreleg or hind leg out of the womb, that limb is forbidden forever, whether the limb is cut off before, or after, shehitah is performed on the mother. Even if the limb was  withdrawn back into the womb and shehitah was then performed on the mother, or if the fetus was born and lived for several years, the limb extended from the womb is forbidden as a tereiphah.

The Keseph Mishneh writes concerning this ruling that it pertains to every fetus that extends a limb, even one whose mother was not slaughtered prior to birth of the fetus, but that the ruling is mistaken, because most animals extend one of their limbs from the womb before their birth. Even though some authorities confirm that the Rambam meant to say what the Keseph Mishnah denies the Rambam meant, the Keseph Mishneh insists that the Rambam did not mean to say that a limb extended from the womb before birth is thereafter forbidden.

But the Rambam’s opinion actually follows the opinion of the Sages who state (Hullin 72a), in opposition to R. Meir, that the extended limb of a fetus is considered a tereiphah based on the verse “ובשר בשדה טרפה”, implying that the status of tereiphah devolves immediately on any limb that crosses its natural boundary — the womb. And the issue between in dispute is whether the concept of birth can pertain to a single limb (יש לידה לאברים) or whether it applies only to a complete organism. R. Meir believes that a single limb can be born, so that, without the verse “ובשר בשדה טרפה”, we know that a limb extended from the mother’s womb is prohibited, because, upon emerging from the womb, the limb is no longer considered a part of the unborn fetus in the womb. A shehitah subsequently performed on the mother, which renders the unborn fetus permissible to be eaten without a shehitah of its own, cannot render the extended limb permissible, so that the status of eiver min ha-hai, which, like neveilah, imparts ritual impurity, devolves upon the extended limb. But the Sages, disagreeing with R. Meir, believe that an extended limb, still being attached to the fetus, cannot be born independently of the fetus. An extended limb would therefore not be treated differently from the fetus, were it not for the verse “ובשר בשדה טרפה”, which teaches us that the extended limb, having crossed its natural boundary, is prohibited as a tereiphah. But when the fetus is born normally, even if one of its limbs was extended from the womb before the rest of the fetus, the subsequent birth of the fetus confirms that the entire fetus was born at the same time, so that the single extended limb is not considered to have crossed its natural boundary and does not have the status of a tereiphah.

The Kesseph Mishneh therefore need not have been troubled that it is commonplace for a fetus to extend a limb outside the womb, because, in ruling that an extended limb has the status of a tereiphah even “if the fetus was born and lived for several years,” the Rambam was referring only to an extended limb that was withdrawn back into the womb before the fetus was born, and the withdrawal of an extended limb back into the womb before birth is certainly not commonplace.

The Rambam was compelled to make this ruling by the law of a ben paqu’ah (a live fetus found in the womb of an animal upon which shehitah had been performed), because the Rambam holds the opinion that once a ben paqu’ah steps on the ground, the shehitah performed on the mother no longer renders its flesh permissible to be eaten, and a Biblical requirement to perform shehitah devolves on the ben paqu’ah before its flesh may be eaten. Here is ruling of the Rambam Ma’akhalot Assurot (5:14)

If a live fetus was found in the womb of an animal upon which shehitah had been performed, even if it completed its entire nine-month gestation in the womb and is certainly viable, shehitah does not have to be performed upon the live fetus before its flesh may be eaten, the shehitah performed on the mother being sufficient. But if the newborn takes a step on the ground, then shehitah must be performed before its flesh may be eaten.

The Kesseph Mishnah adds

And this shehitah is required only rabbinically for appearances (מראית עיין). And the Rambam writes in his commentary on the Mishnah, “and the newborn does not require inspection, by which he means to say that the possibility of finding the newborn to be a tereiphah is not a concern, because the newborn, although alive, is considered to have had a valid shehitah already performed on it.

But obviously if the Rambam believed that the obligation to perform shehitah on a newborn that took a step on the ground after being found in the womb of its mother is merely rabbinic, he certainly would not have written that shehitah is required without explicitly stating that the obligation is for appearances, because the Rambam always distinguishes meticulously between Biblical and rabbinic obligations, and especially those obligations that are merely for appearances.

The Kesseph Mishnah also erred in attributing to the Rambam the position of the other Rishonim that once the newborn steps on the ground, shehitah is required only for appearances, and that, because the newborn is not susceptible to becoming a tereiphah, no inspection is required after shehitah is performed on it. If the interpretation of the Kesseph Mishnah were correct, the Rambam should have also codified this interpretation when codifying the law of a ben paqu’ah in the Yad Ha-Hazaqah. But in his commentary on the Mishnah, the Rambam writes as follows:

Although this living nine-month fetus may be eaten without a shehitah being performed upon it, its fat and its blood (חלבו ודמו) may not be eaten according to the opinion of the Sages. And it requires no inspection for fatal defects, because such defects would not render it unfit for consumption, its status already being that it had a valid shehitah performed upon it even though it is still alive. And the law follows the opinion of the Sages unless it steps on the ground, while the opinion of Rebi Shimon Shezuri that the newborn may be eaten even after it has stepped on the ground is not authoritative.

The Rambam did not mention taking a step on the ground until the end of the Mishnah, so that it is only once the newborn does step on the ground that the shehitah performed on the mother does not render the flesh of the newborn fit for consumption without a separate shehitah being performed on the newborn. Nevertheless, the fat and the blood of a newborn that has not stepped on the ground is prohibited. The Rambam therefore had to resolve a question about the status of a newborn suffering from a congenitally fatal defect. Inasmuch as its fat and blood are prohibited, being considered part of the newborn rather than just an organ of the mother, it would have seemed that a congenitally fatal defect of the newborn should render the newborn a tereiphah in which case its flesh would be prohibited despite the shehitah that had been performed on its mother. But the Rambam teaches us that although the fat and the blood of the newborn are prohibited because the newborn is considered an entity distinct and separate from its mother, this status has no implication for the susceptibility of the newborn to become a tereiphah, because tereiphah is the first stage of neveilah, the prohibitions of tereiphah and neveilah being subsumed under a single heading and therefore being combined if the quantity of neither is sufficient to require lashes to be administered (Ma’akhalot Assurot 4:17). Accordingly, if the prohibition of neveilah is inapplicable to a dead fetus in the womb of a mother upon which shehitah has been performed, how could the flesh of a live newborn with a fatal defect be prohibited as a tereiphah?

However, the Tosaphists and the other Rishonim who disagree with the Rambam, believing that the fat of the fetus is permitted, would certainly say that a congenital fatal defect of the fetus does not render the fetus a tereiphah. But once the newborn steps on the ground, thereby creating, according to the Tosaphists et al., a rabbinic obligation to perform shehitah on the newborn before its flesh may be eaten, the question arises whether a fatal defect that befalls the newborn after it takes a step would render the flesh of the newborn unfit to be eaten. The Tosaphists conclude that, notwithstanding the defect, the flesh of the newborn is permissible, because the fatal defect is not obvious and shehitah is required only for appearances. But these questions were not problematic for the Rambam, inasmuch as he believes that the requirement to perform shehitah on a ben paqu’ah that has stepped on the ground is Biblical, not rabbinic, so that a fatal defect occurring after the newborn steps on the ground would render its flesh Biblically prohibited.

Reference was made above to the comment from the Rambam’s commentary on the Mishnah at Hullin 74b in which R. Shimon Shezuri and the Sages argue about the permissibility of a ben paqu’ah. R. Mesharshia and Abaye at Hullin 75b disagree about the basis for the dispute between R. Shimon Shezuri and the Sages. The disagreement between R. Mesharshia and Abaye is recorded in the Gemara after R. Kahana’s statement that R. Shimon Shezuri and the Sages disagreed only in a case in which the ben paqu’ah has stepped on the ground. According to the Rambam, R. Mesharshia interprets R. Kahana’s statement to mean that the Sages consider the requirement to perform shehitah on a ben paqu’ah that has stepped on the ground to be Biblical while R. Shimon Shezuri maintains that the shehitah performed on ben paqu’ah’s mother eliminates the Biblical obligation to perform shehitah on it even if it does step on the ground. Abaye disagrees with R. Mesharshia, maintaining that the Sages hold the obligation to perform shehitah on a ben paqu’ah to be rabbinic and only for appearances. The Rambam codifies the halakhah according to the opinion of the Sages, against that of R. Shimon Shezuri, and according to R. Mesharshia’s understanding of the dispute, against that of Abaye, that the obligation to perform shehitah on a ben paqu’ah that has stepped on the ground is Biblical not rabbinic.

The Rambam was compelled to explain in Ma’akhalot Assurot 5:9 that the prohibition against an extended limb is unrelated to shehitah, but is instead inferred from a separate Biblical prohibition inferred from the verse “ובשר בשדה טרפה”, because he believes that, once a ben paqu’ah steps on the ground, the shehitah performed on its mother no longer permits the flesh of the ben paqu’ah to be consumed, so that, from that moment, the ben paqu’ah is covered by the Biblical obligation to perform shehitah. If there is a Biblical obligation to perform shehitah on the ben paqu’ah once it steps on the ground, why would we not also conclude that the Biblical obligation to perform shehitah on an animal with a limb extended from the womb and then withdrawn back into the womb would also render that extended limb permissible to be eaten? Because the Rambam infers from the existence of a Biblical obligation to perform shehitah on a ben paqu’ah that has stepped on the ground that if a shehitah is performed on an animal whose limb was extended from the womb shehitah should indeed render the extended limb of the animal fit to be eaten.

To account for the prohibition on the extended limb the Rambam had to identify another source for the prohibition against eating the flesh of both a limb extended before birth and of a mangled limb hanging from an animal (eiver ha-meduldal), the source being the verse “ובשר בשדה טרפה לא תאכלו”. But although the prohibition against an extended limb is Biblical, it is not punishable by lashes, because the prohibition inferred from that verse is one of multiple separate prohibitions inferred from the verse (lav she-biklalot) and is therefore exempt from lashes.

But why, indeed, is there a Biblical obligation to perform shehitah on a ben paqu’ah that takes a step if there is no obligation to perform shehitah on a ben paqu’ah that has not taken a step? Before entry into the Land, the Biblical requirement to perform shehitah (or nehirah) was not satisfied until the actual death of the animal. It was only upon entry into the Land, when nehirah was invalidated as a method of slaughter, that shehitah rendered the flesh of an animal permissible even while the animal was still convulsing in its death throes. But along with the leniency that shehitah takes immediate effect, there was an added requirement that both simanim of a four-legged animal and at least one siman of a fowl had to be cut. So, although the death of the animal was no longer strictly necessary for shehitah to be effective, shehitah had to be performed in such a way that the death of the animal would be highly likely within a short time, not exceeding 24 hours. It therefore became necessary that the shehitah performed on a mother carrying a fetus cause the mother to die within a short time. Thus, if the death of the mother was not necessary before its flesh could be eaten, it was also not necessary that the ben paqu’ah should die before the flesh of the ben paqu’ah would be permitted as a result of the shehitah performed on its mother.

However, just as the death of mother had to be imminent in order for its flesh to be permitted as a result of shehitah, the shehitah performed on the mother could be effective on the ben paqu’ah only if it was already dead or if the imminent death of the newborn could be expected. But if, after the ben paqu’ah takes a step, the shehitah performed on its mother is evidently not likely to cause the imminent death of the newborn, how can it be that such a shehitah could render the flesh of the newborn permissible to be eaten? Thus, once the newborn takes a step, it can no longer be presumed that the shehitah performed on the mother will cause the imminent death of the newborn, so it becomes impossible to regard that shehitah as effective in rendering the flesh of the newborn permissible to be eaten.