Halakhah for Keritot 8:65

From the laws of the commandment is, for example, that which they, may their memory be blessed, explained (Keritot 4b) that the prohibition of forbidden fat is only with the three beasts in Scripture - the ox, the sheep and the goat. And one is liable for the chelev of these three, whether they are fit (kosher), torn or carcasses. But the chelev of other types of animals - whether impure or pure - is like its meat. And so [too,] there is no prohibition of chelev in the fetus that is called the embryo that is in the innards of the three beasts mentioned. And therefore, they said (Chullin 74b) [about] one who slaughters an animal and found an embryo in it, [that] all of its chelev is permitted - and even if he found it alive. But if it finished its months and he found it alive - even though it did not hover over the ground and it does not require slaughter - its chelev is forbidden, and we are liable excision for it. And behold, its law is like [adult] beasts regarding its chelev. And hence we must remove all the fibers and all of the forbidden membranes from it. This is the opinion of Rambam, may his memory be blessed, (Mishneh Torah, Laws of Forbidden Foods 7:3) regarding an embryo that has finished its months - that there is a liability for excision with its chelev. But the majority of the commentators disagree with this and say that its chelev is permissible. And the words of the Gemara (Chullin 92b) decide like them. As behold we found Rabbi Meir and Rabbi Yehudah disagreeing about its chelev; and Rabbi Yehudah - whom we follow - is the one that permits it.

And do not think to say that this negative commandment of "You may not" is a general prohibition, as each and every matter is a negative commandment on its own. And so is it explained in Tractate Makkot (it should say Keritot 4b), "If he ate tithe of grain, wine and oil, he is liable for each and every one." And it challenges there, "And do we administer lashes for a general prohibition?" And it answers it, "The verse is superfluous. How is it? It is written (Deuteronomy 12:23), 'And you shall eat in front of the Lord, your God [...] the tithe of your grain, your wine and your oil.'" [This discussion continues in Makkot 18a:] "Let the [Torah] write, 'You may not eat them in your gates.' Why do I need the [Torah] to enumerate all of them here? [Hence] we understand from it [that it is] to designate for them a negative commandment for each and every one." And this verse of "And you shall eat" is at the end of this Order.