On 43b, Tosefos d"h biveheimah, he asks on Rashi in Niddah 24a. Rashi there brings R' Chanina ben Antigonus - who explains gibein as having two backs/spines - as being a mishnah about the momin on animals. Rabbeinu Tam complains there and here: It's a mishnah here in the seventh perek, and thus obviously applies to cohanim, not to animals. That's what the seventh perek is about.
Seems like a devastating question, and a ridiculous mistake.
I'm wonder if the answer for Rashi is that it depends on what the word gibein means. The mishnah first quotes the tana kama, who says that it means some problem about the eyebrows. That is indeed not a full-fledged mum, only applies to cohanim. But then R' Chanina ben Antigonus argues and says that it means two spines. That's really serious, a treifah (or worse, see there), and one that is quite visible. According to him, it's a full-fledged mum.
The reason that he didn't say it in the previous perek is because he is commenting on the tana kama here.
Seems like a devastating question, and a ridiculous mistake.
I'm wonder if the answer for Rashi is that it depends on what the word gibein means. The mishnah first quotes the tana kama, who says that it means some problem about the eyebrows. That is indeed not a full-fledged mum, only applies to cohanim. But then R' Chanina ben Antigonus argues and says that it means two spines. That's really serious, a treifah (or worse, see there), and one that is quite visible. According to him, it's a full-fledged mum.
The reason that he didn't say it in the previous perek is because he is commenting on the tana kama here.