Pesachim 85A

לא, הכי קאמר: אחד עצם שיש עליו כזית בשר מבחוץ, ואחד עצם שאין עליו כזית בשר מבחוץ, ויש עליו כזית בשר מבפנים במקום שבירה.

No, that is not what it means to say. Rather, this is what it is saying: It is prohibited to break both a bone upon which there is an olive-bulk of meat on the outside and a bone upon which there is not an olive-bulk of meat on the outside, but there is an olive-bulk of meat, i.e., bone marrow, on the inside at the place of the break.

והתניא: ״ועצם לא תשברו בו״⁠ — אחד עצם שיש בו מוח, ואחד עצם שאין בו מוח. ומה אני מקיים ״ואכלו את הבשר בלילה הזה״⁠ — בבשר שעל גבי העצם.

And as a proof, the Talmud cites that which was taught in a baraita with regard to the verse: “And you should not break a bone in it” (Exodus 12:46). This prohibition includes both a bone in which there is marrow and a bone in which there is no marrow. How do I establish the positive mitzva expressed in the verse: “And they should eat the meat on that night” (Exodus 12:8)? It is to be fulfilled exclusively with meat that is on the bone.

או אינו אלא בבשר שבתוך העצם, ומה אני מקיים ״ועצם לא תשברו בו״⁠ — בעצם שאין בו מוח, אבל בעצם שיש בו מוח ⁠— שובר ואוכל. ואל תתמה, שהרי יבא עשה וידחה לא תעשה.

Or perhaps it means only that the positive mitzva also applies to the marrow meat that is inside the bone. And if so, how do I establish the prohibition: And you should not break a bone in it? It is referring specifically to a bone that does not have marrow. However, in the case of a bone that does have marrow, one may break and eat the marrow. And do not be surprised that one may violate the prohibition of breaking a bone in order to eat the marrow, as it is possible to say that the positive mitzva to eat the meat comes and overrides the prohibition prohibiting one to break a bone, in accordance with the general principle that positive mitzvot override negative mitzvot.