קורבנות
הלכות בכורות
פרק ד

Halacha

הלכה א
בֶהֱמַת הַשֻּׁתָּפִין חַיֶּבֶת בִּבְכוֹרָה. לֹא נֶאֱמַר (דברים יב יז) (דברים יד כג) "בְּקָרְךָ וְצֹאנֶךָ" אֶלָּא לְמַעֵט שֻׁתָּפוּת הַנָּכְרִי שֶׁאִם הָיָה שֻׁתָּף בַּפָּרָה אוֹ בָּעֵבָּר אֲפִלּוּ הָיָה לַנָּכְרִי אֶחָד מֵאֶלֶף בָּאֵם אוֹ בַּוָּלָד הֲרֵי זֶה פָּטוּר מִן הַבְּכוֹרָה. הָיָה לוֹ בְּאֶחָד מִשְּׁנֵיהֶם אֵיבָר אֶחָד כְּגוֹן יָד אוֹ רֶגֶל. רוֹאִין כָּל שֶׁאִלּוּ יֵחָתֵךְ וְהָיָה בַּעַל מוּם הֲרֵי זֶה פָּטוּר. וְאִם אֶפְשָׁר שֶׁיֵּחָתֵךְ אֵיבַר הַנָּכְרִי וְלֹא יִפָּסֵל. הֲרֵי זֶה חַיָּב בִּבְכוֹרָה:
כסף משנה
1.
There is an obligation to apply the laws of a firstborn to an animal owned by partners. The terms "your cattle and your sheep" was used only to exclude an animal owned in partnership with a gentile. For if a gentile was a partner in the ownership of a cow or of the fetus it is carrying - even if the gentile owns only a thousandth share of the mother or the offspring, it is exempt from the requirements pertaining to the firstborn.
If the gentile owned one specific limb of one of them, e.g., a forefoot or a hindfoot, any limb which if cut off that limb would render the animal as blemished, exempts it. If the limb owned by the gentile could be cut off without disqualifying the animal as a firstborn, it is obligated in the laws of the firstborn.

הלכה ב
הַלּוֹקֵחַ עֻבַּר פָּרָתוֹ שֶׁל נָכְרִי. אוֹ הַמּוֹכֵר עֻבַּר פָּרָתוֹ לְנָכְרִי. אַף עַל פִּי שֶׁאֵינוֹ רַשַּׁאי הֲרֵי זֶה פָּטוּר מִן הַבְּכוֹרָה. וְאֵין קוֹנְסִין אוֹתוֹ עַל דָּבָר זֶה:
כסף משנה
2.
When a person purchases a fetus being carried by a cow owned by a gentile or he sells a fetus being carried by his cow to a gentile, even though he is not permitted to do so, the fetus is exempt from the requirements of the firstborn. He is not penalized because of this matter.

הלכה ג
הַמְקַבֵּל בְּהֵמָה מִן הַנָּכְרִי לִהְיוֹת מְטַפֵּל בָּהּ וְהַוְּלָדוֹת בֵּינֵיהֶם. אוֹ נָכְרִי שֶׁקִּבֵּל מִיִּשְׂרָאֵל כָּזֶה. הֲרֵי אֵלּוּ פְּטוּרִים מִן הַבְּכוֹרָה שֶׁנֶּאֱמַר (שמות יג ב) "פֶּטֶר כָּל רֶחֶם בִּבְנֵי יִשְׂרָאֵל" עַד שֶׁיִּהְיֶה הַכּל מִיִּשְׂרָאֵל:
כסף משנה
3.
When a person receives an animal from a gentile to care for it and the offspring would be shared or a gentile receives an animal from a Jew under such an arrangement, the offspring are exempt from the requirements of firstborn animals.This is implied by Exodus 13:2: "All the first issue of the womb among the children of Israel," i.e., everything must belong to a Jew.

הלכה ד
הַמְקַבֵּל צֹאן מִן הַנָּכְרִי בְּמָמוֹן קָצוּב וּפָסַק עִמּוֹ שֶׁיִּהְיֶה הַשָּׂכָר בֵּינֵיהֶם וְאִם פִּחֲתוּ פִּחֲתוּ לְיִשְׂרָאֵל. אַף עַל פִּי שֶׁבִּרְשׁוּת יִשְׂרָאֵל הֵם וַהֲרֵי הֵם כְּקִנְיָנוֹ הוֹאִיל וְאִם לֹא יִמְצָא הַנָּכְרִי אֶצְלוֹ מָמוֹן אַחֵר לִגְבּוֹת מִמֶּנּוּ יִגְבֶּה מִן הַבְּהֵמוֹת הָאֵלּוּ וּמִוַּלְדוֹתֵיהֶן נַעֲשָׂה כְּמוֹ שֶׁיֵּשׁ לוֹ אַחֲרָיוּת עֲלֵיהֶן וְעַל וַלְדוֹתֵיהֶן וַהֲרֵי יַד הַנָּכְרִי בְּאֶמְצַע וּפְטוּרִין מִן הַבְּכוֹרָה הֵם וּוַלְדוֹתֵיהֶן. אֲבָל וַלְדֵי וְלָדוֹת חַיָּבִין שֶׁהֲרֵי שֶׁל יִשְׂרָאֵל הֵם וְאֵין לַנָּכְרִי רְשׁוּת עֲלֵיהֶן:
כסף משנה
4.
The following laws apply when a Jew receives sheep from a gentile at a fixed price and agreed that the profit will be split between them, but if the worth of the animal is reduced, the loss is born by the Jew alone. Even though the sheep are in the domain of the Jew and are his property, since if the gentile will not find any other resources to collect his debt for the lost sheep from him, he will take these sheep and their offspring, it is considered as if he has a lien on them and their offspring. Thus the gentile is considered as having a share of them and they and their offspring are exempt from the requirements of the firstborn. The offspring of their offspring, however, are liable for they belong to the Jew and the gentile has no authority over them.

הלכה ה
יִשְׂרָאֵל שֶׁנָּתַן מָעוֹת לְנָכְרִי וְקָנָה לוֹ בָּהֶן בְּהֵמָה מִנָּכְרִי בְּדִינֵיהֶן אַף עַל פִּי שֶׁלֹּא מָשַׁךְ קָנָה וְחַיֶּבֶת בִּבְכוֹרָה. וְכֵן אִם קָנָה הַנָּכְרִי מִיִּשְׂרָאֵל בְּדִינֵיהֶם וְנָתַן מָעוֹת אַף עַל פִּי שֶׁלֹּא מָשַׁךְ קָנָה וּפְטוּרָה מִבְּכוֹרָה:
כסף משנה
5.
When a Jews pays money to a gentile and thus acquires an animal from a gentile according to their law, even though he did not perform meshichah,he acquires the animal and the requirements of the firstborn apply to its offspring. Similarly, if a gentile acquired an animal from a Jew according to their laws and paid money, he acquires it even though he did not perform meshichah and its offspring are exempt from the requirements of the firstborn.

הלכה ו
גֵּר שֶׁנִּתְגַּיֵּר וְאֵין יָדוּעַ אִם עַד שֶׁלֹּא נִתְגַּיֵּר יָלְדָה פָּרָתוֹ אוֹ אַחַר שֶׁנִּתְגַּיֵּר הֲרֵי זֶה בְּכוֹר מִסָּפֵק:
כסף משנה
6.
When a gentile converts and it is not known whether his cow gave birth before he converted or afterwards, it is considered a firstborn because of the doubt.

הלכה ז
הַלּוֹקֵחַ בְּהֵמָה מִן הַנָּכְרִי וְאֵין יָדוּעַ אִם בִּכְּרָה אוֹ לֹא בִּכְּרָה וְיָלְדָה אֶצְלוֹ הֲרֵי זֶה סְפֵק בְּכוֹר וְיֵאָכֵל בְּמוּמוֹ לַבְּעָלִים וְאֵינוֹ לַכֹּהֵן שֶׁהַמּוֹצִיא מֵחֲבֵרוֹ עָלָיו הָרְאָיָה:
כסף משנה
7.
When a person purchases an animal from a gentile and does not know whether it gave birth already or not, if it gives birth in his possession, the offspring is considered a firstborn because of the doubt. It should be eaten by its masters after it becomes blemished, but is not given to a priest. The rationale is that when a person desires to expropriate property from a colleague, the burden of proof is on the plaintiff.

הלכה ח
לָקַח בְּהֵמָה מֵינִיקָה מִן הַנָּכְרִי אֵינוֹ חוֹשֵׁשׁ שֶׁמָּא בְּנָהּ שֶׁל אַחֶרֶת הִיא מֵינִיקָה אֶלָּא הֲרֵי זוֹ בְּחֶזְקַת שֶׁיָּלְדָה. וַאֲפִלּוּ הָיָה זֶה שֶׁמֵּינִיקָה כְּמוֹ מִין אַחֵר וַאֲפִלּוּ כְּמִין חֲזִיר הֲרֵי זוֹ פְּטוּרָה מִן הַבְּכוֹרָה. וְכֵן בְּהֵמָה שֶׁהִיא חוֹלֶבֶת פְּטוּרָה מִן הַבְּכוֹרָה שֶׁרֹב הַבְּהֵמוֹת אֵינָן חוֹלְבוֹת אֶלָּא אִם כֵּן כְּבָר יָלְדוּ:
כסף משנה
8.
When a person purchases an animal that is giving suck from a gentile, he need not suspect that it is giving suck to the offspring of another animal. Instead, we operate under the assumption that it has already given birth. Even if the animal to which it is giving suck is like another species, even if it is like a pig, it is exempt from the requirements of the firstborn.
Similarly, the offspring of an animal that is providing milk is exempt from the requirements of the firstborn. The rationale is that we rely on the assumption that most animals do not provide milk unless they have given birth previously.

הלכה ט
הַלּוֹקֵחַ בְּהֵמָה מִיִּשְׂרָאֵל הֲרֵי זוֹ בְּחֶזְקַת שֶׁבִּכְּרָה עַד שֶׁיּוֹדִיעוֹ הַמּוֹכֵר שֶׁעֲדַיִן לֹא יָלְדָה. שֶׁאֵין הַיִּשְׂרָאֵל שׁוֹתֵק וְגוֹרֵם לוֹ לֶאֱכל קָדָשִׁים בַּחוּץ וַדַּאי שֶׁבִּכְּרָה וּלְפִיכָךְ מְכָרָהּ סְתָם:
כסף משנה
9.
When a person purchases an animal from a fellow Jew, we operate under the assumption that it already gave birth unless the seller states that it did not give birth yet. The rationale is that we assume a Jew will not remain silent and cause a fellow Jew to partake of a consecrated animal outside the Temple Courtyard. Hence we conclude that it certainly gave birth previously. Therefore the owner sold the mother without any qualification.

הלכה י
בְּהֵמָה דַּקָּה שֶׁהִפִּילָה עֻבָּר שֶׁעֲדַיִן לֹא נִתְבָּאֵר צוּרָתוֹ הַרְבֵּה וְנִכֶּרֶת לַכּל וְזֶהוּ הַנִּקְרָא טִנּוּף. אִם אָמְרוּ הָרוֹעִים עֻבָּר הוּא אֶלָּא שֶׁנִּפְסְדָה צוּרָתוֹ הֲרֵי זוֹ פְּטוּרָה מִן הַבְּכוֹרָה וְצָרִיךְ לְהַרְאוֹתוֹ לְרוֹעֶה חָכָם. לְפִיכָךְ הַלּוֹקֵחַ בְּהֵמָה מִן הַנָּכְרִי אֲפִלּוּ הָיְתָה קְטַנָּה וְיָלְדָה אֶצְלוֹ בְּתוֹךְ שְׁנָתָהּ הֲרֵי זֶה סְפֵק בְּכוֹר שֶׁמָּא טִנּוּף הִפִּילָה בִּרְשׁוּת הַנָּכְרִי. וְכֵן בְּהֵמָה גַּסָּה שֶׁהִפִּילָה שִׁלְיָא הֲרֵי זוֹ סִימָן וָלָד שֶׁאֵין שִׁלְיָא בְּלֹא וָלָד וְנִפְטְרָה מִן הַבְּכוֹרָה. וּמֻתָּר לְהַשְׁלִיךְ אוֹתָהּ הַשִּׁלְיָא לַכְּלָבִים שֶׁאֵין מִתְקַדֵּשׁ בִּבְכוֹרָה אֶלָּא זָכָר וְחֶזְקַת הַנּוֹלָדִים מֶחֱצָה זְכָרִים וּמֶחֱצָה נְקֵבוֹת. וּכְבָר בֵּאַרְנוּ שֶׁהַזָּכָר שֶׁאֵין בּוֹ מִקְצָת סִימָנֵי אִמּוֹ אֵינוֹ מִתְקַדֵּשׁ בִּבְכוֹרָה וְנִמְצָא מִעוּט הַנּוֹלָדִים הֵן הַמִּתְקַדְּשִׁין בִּבְכוֹרָה וְאֵין חוֹשְׁשִׁין לְמִעוּט. אֲבָל בֶּהֱמַת קָדָשִׁים שֶׁהִפִּילָה שִׁלְיָא תִּקָּבֵר [שֶׁהַנְּקֵבוֹת בָּהּ כִּזְכָרִים]:
כסף משנה
10.
The following laws apply when a small animal miscarries and discharges a fetus whose form has not become very distinct and evident to all. It is called a tinuf. If the shepherds say: "It was a fetus, but its form has become marred," the future offspring of this animal is exempt from the requirements of the firstborn. It must, however, be shown to a shepherd who is knowledgeable.
Therefore if one purchases an animal from a gentile, even if it was small and gave birth within its first year of life, the offspring is considered as a firstborn of doubtful status, because it is possible that it discharged a tinuf while owned by the gentile.
Similarly, when a large animal discharges a placenta, it is a sign that it carried a fetus, for a placenta is never formed without a fetus and the offspring is exempt from the requirements of the firstborn. It is permitted to throw that fetus to the dogs for the following reasons. Only a male is sanctified as a firstborn. We assume that offspring are half male and half female. We have already explained that a male that does not have some of the distinguishing signs of its mother is not consecrated as a firstborn. Thus the lesser portion of animals' first offspring is consecrated as a firstborn. Hence since the probability is less than half, it is not considered. When, by contrast, a consecrated animal discharges a placenta, it must be buried. For the female offspring are bound by the same laws as the male.

הלכה יא
בְּהֵמָה גַּסָּה שֶׁהִפִּילָה חֲרָרַת דָּם הֲרֵי זוֹ נִפְטְרָה מִן הַבְּכוֹרָה שֶׁחֶזְקָתָהּ שֶׁהַוָּלָד בְּתוֹכָהּ וְרָבָה עָלָיו הַדָּם וְהִפְסִידוֹ וּבִטְּלוֹ. וְקוֹבְרִין חֲרָרָה זוֹ כְּמוֹ נֵפֶל מְבַכֶּרֶת אַף עַל פִּי שֶׁאֵין חֲרָרָה זוֹ קְדוֹשָׁה. וְלָמָּה קוֹבְרִין אוֹתָהּ כְּדֵי לְפַרְסֵם הַדָּבָר שֶׁנִּפְטְרָה מִן הַבְּכוֹרָה:
כסף משנה
11.
When a large animal discharges a flow of blood, the future offspring of this animal is exempt from the requirements of the firstborn, for we assume that there was an offspring in it, but there was much more blood and it lost its form and its existence was nullified. We must bury the flow of blood like a stillborn firstborn animal, even though this flow of blood has no consecrated quality. Why is it buried? In order to publicize the matter that the offspring of this animal was exempted from the requirements of the firstborn.

הלכה יב
כְּבָר בֵּאַרְנוּ בְּעִנְיַן נִדָּה שֶׁהַוָּלָד בָּאָדָם נִגְמָר לְאַרְבָּעִים יוֹם וְהַמַּפֶּלֶת לְפָחוֹת מֵאַרְבָּעִים אֵינוֹ וָלָד. אֲבָל וְלַד בְּהֵמָה לֹא עָמְדוּ חֲכָמִים עַל מִנְיַן הַיָּמִים שֶׁיִּגָּמֵר בּוֹ. אֲבָל אָמְרוּ שֶׁהַמַּפֶּלֶת טִנּוּף אֵינָהּ מִתְעַבֶּרֶת אַחֲרָיו וְלֹא מְקַבֶּלֶת וָלָד אַחֵר לְפָחוֹת מִשְּׁלֹשִׁים יוֹם:
כסף משנה
12.
We already explained with regard to the concept of a woman in the niddah state that the form of a human fetus is completed on the fortieth day after conception. Thus when a woman miscarries after less than 40 days, she is not considered to have miscarried a fetus. Our Sages did not, however, conclusively determine the amount of days in which the form of an animal fetus is completed. They did, however, say that an animal which discharges a tinuf does not become pregnant, nor does it carry another fetus until after 30 days.

הלכה יג
בְּהֵמָה שֶׁיָּצְאָה מְלֵאָה וּבָאָה רֵיקָנִית הַבָּא אַחַר כֵּן בְּכוֹר מִסָּפֵק שֶׁמָּא דָּבָר שֶׁאֵינוֹ פּוֹטֵר בִּבְכוֹרָה הִפִּילָה. וְאֵין לְנִפְלֵי בְּהֵמָה פְּטִירַת רֶחֶם עַד שֶׁיַּעֲגִילוּ רֹאשׁ כְּפִיקָה שֶׁל עֵרֶב:
כסף משנה
13.
When an animal left pregnant and returned empty, her next offspring is considered as a firstborn because of the doubt involved. Perhaps what she discharged was not an entity that exempts her offspring from the requirements of the firstborn. A fetus that was miscarried is not considered to have "opened its mother's womb" unless its head was the size of top of the needle of the woof.

הלכה יד
מַבְכֶּרֶת הַמַּקְשָׁה לֵילֵד מְחַתֵּךְ אֵיבָר וּמַשְׁלִיךְ לַכְּלָבִים וְהַבָּא אַחֲרָיו בְּכוֹר. יָצָא רֻבּוֹ הֲרֵי זֶה יִקָּבֵר וְנִפְטְרָה מִן הַבְּכוֹרָה. וְאִם חָתַךְ אֵיבָר וְהִנִּיחוֹ אֵיבָר וְהִנִּיחוֹ עַד שֶׁהִשְׁלִים רֻבּוֹ הֲרֵי כָּל הָאֵיבָרִים צְרִיכִין קְבוּרָה. וְנִפְטְרָה מִן הַבְּכוֹרָה כֵּיוָן שֶׁיָּצָא רֻבּוֹ בֵּין שָׁלֵם בֵּין מְחֻתָּךְ וַהֲרֵי הוּא לְפָנֵינוּ נִתְקַדֵּשׁ לְמַפְרֵעַ:
כסף משנה
14.
When an animal that is having difficulty giving birth to its firstborn, the offspring may be cut up limb by limb and the limbs extracted and thrown to the dogs immediately. The offspring that follows is a firstborn.
If the greater portion of a fetus emerges at one time, it must be buried and the future offspring of the mother is exempted from the requirements of the firstborn.
If one cut off a limb, extracted it, put it aside, cut off another limb, until the greater portion of the fetus is completed, all of the limbs are required to be buried and the future offspring of the mother is exempted from the requirements of the firstborn. [The rationale is that] since the greater part of the animal was taken out - whether whole or cut in pieces - and it is present before us, it becomes consecrated retroactively.

הלכה טו
יָצָא שְׁלִישׁ וּמְכָרוֹ לְנָכְרִי וְחָזַר וְיָצָא שְׁלִישׁ אַחֵר. נִתְקַדֵּשׁ לְמַפְרֵעַ וְנִפְטְרָה מִן הַבְּכוֹרָה. יָצָא שְׁלִישׁ דֶּרֶךְ דֹּפֶן וּשְׁנֵי שְׁלִישִׁים דֶּרֶךְ רֶחֶם אֵינוֹ קָדוֹשׁ שְׁהָרֹב הָרִאשׁוֹן לֹא יָצָא דֶּרֶךְ רֶחֶם וּלְמַפְרֵעַ הוּא מִתְקַדֵּשׁ:
כסף משנה
15.
When a third of the fetus emerged and it was sold to a gentile and then a second third emerged, it is consecrated retroactively and the future offspring of the mother is exempted from the requirements of the firstborn.
If a third of the offspring was removed by Caesarian section and, afterwards, two thirds emerged through the womb, it is not consecrated. The rationale is that the first larger portion did not emerge from the womb and the consecration would have been brought about retroactively.

הלכה טז
יָצָא מִעוּט אֵיבָר גָּדוֹל וַהֲרֵי זֶה הַיּוֹצֵא רֻבּוֹ שֶׁל עֻבָּר נִפְטַר מִן הַבְּכוֹרָה וְיִקָּבֵר הַיּוֹצֵא. יָצָא חֲצִי הָעֻבָּר וְהוּא רֻבּוֹ שֶׁל אֵיבָר הַיּוֹצֵא הֲרֵי זֶה סָפֵק אִם נִפְטְרָה מִן הַבְּכוֹרָה אוֹ לֹא נִפְטְרָה לְפִיכָךְ הַבָּא אַחֲרָיו סְפֵק בְּכוֹר:
כסף משנה
16.
The following laws apply when the lesser portion of one limb emerges from the womb together with the greater portion of the animal. Since the portion that emerges constitutes the greater portion of the fetus, the future offspring of the mother is exempted from the requirements of the firstborn and the portion that emerged should be buried..
If only half of the fetus emerges from the womb together with the greater portion of one limb, there is an unresolved doubt whether the future offspring of the mother is exempted from the requirements of the firstborn or not. Therefore the next offspring is a firstborn of doubtful status.

הלכה יז
בְּכוֹר שֶׁכְּרָכוֹ בְּסִיב וְהוֹצִיאוֹ וְלֹא נָגַע בָּרֶחֶם אוֹ שֶׁכְּרָכוֹ בְּשִׁלְיַת בְּהֵמָה אַחֶרֶת אוֹ שֶׁנִּכְרְכָה עָלָיו אֲחוֹתוֹ וְיָצָא הוֹאִיל וְלֹא נָגַע בָּרֶחֶם מִכָּל מָקוֹם הֲרֵי זֶה סְפֵק בְּכוֹר:
כסף משנה
17.
When a firstborn was wrapped in a fiber and removed from the womb without touching the womb or it was wrapped with a placenta of another animal or it was wounded up together with its sister and emerged, since it did not touch the womb, it is considered as a firstborn of doubtful status.

הלכה יח
הִדְבִּיק שְׁנֵי רְחָמִים זֶה לָזֶה וְיָצָא מִזֶּה וְנִכְנַס לָזֶה הֲרֵי זֶה סָפֵק אִם נִפְטְרָה מִן הַבְּכוֹרָה הַבְּהֵמָה שֶׁנִּכְנַס בָּהּ הַבְּכוֹר שֶׁהֲרֵי פֶּטֶר רֶחֶם אוֹ לֹא נִפְטְרָה עַד שֶׁיִּפְטֹר רַחְמָהּ וְלָדָהּ:
כסף משנה
18.
If one cleaved the wombs of two animals together and a fetus emerged from one and entered the other, there is an unresolved doubt: Is the future offspring of the animal to whose womb the firstborn entered exempted from the requirements of the firstborn, for its womb was "opened?" Or is it not exempted until it "opens its womb" when giving birth to its own offspring?

הלכה יט
נִפְתְּחוּ כָּתְלֵי בֵּית הָרֶחֶם וְיָצָא הֲרֵי זֶה סָפֵק אִם נְגִיעַת רֶחֶם מְקַדֶּשֶׁת אוֹ אֲוִירוֹ:
כסף משנה
19.
If the walls of the mother's womb opened and the firstborn emerged without touching the walls of the womb, there is an unresolved doubt: Is it consecrated because it touches the walls of the mother's womb? Or is it consecrated because it was in the space of the mother's womb?

הלכה כ
נֶעֶקְרוּ כָּתְלֵי בֵּית הָרֶחֶם [וְנִתְלוּ] בְּצַוָּארוֹ הֲרֵי זֶה סָפֵק אִם בִּמְקוֹמוֹ מְקַדֵּשׁ אוֹ מְקַדֵּשׁ אַף חוּץ לִמְקוֹמוֹ:
כסף משנה
20.
If the walls of the the mother's womb were uprooted from their place and were suspended around the offspring's neck, there is an unresolved doubt: Do they cause the offspring to be consecrated only when they are in their place? Or do they cause it to be consecrated even if they are not in their place.

הלכה כא
נִגְמְמוּ כָּתְלֵי בֵּית הָרֶחֶם אֵינוֹ קָדוֹשׁ. נִפְרַץ מִקְצָתוֹ וְעוֹמֵד מְרֻבֶּה עַל הַפָּרוּץ וְיָצָא דֶּרֶךְ הַפָּרוּץ. אוֹ שֶׁהָיָה הַפָּרוּץ מְרֻבֶּה עַל הָעוֹמֵד וְיָצָא דֶּרֶךְ הָעוֹמֵד הֲרֵי זֶה סְפֵק בְּכוֹר:
כסף משנה
21.
If the flesh supporting the walls of the womb decomposes, the offspring is not consecrated. If the walls of the womb are partially stripped off, but the portion that remained is greater than the portion that was stripped off and the offspring emerged through the open area or the portion that was stripped off is greater than the portion that remained and the offspring emerged through the portion that remained, the offspring is a firstborn of doubtful status.

קורבנות הלכות בכורות פרק ד
Korbanot Bechoros Chapter 4