I noticed the last mishna in Perek 8 is the same topic as beginning mishna in Perek 9.... so why did the perakim divide between them?
hg
1) The Meiri, at the beginning of the 9th chapter of Baba Basra, refers us to what he wrote at the beginning of the Masechta. There he wrote that the Masechta is divided into 6 parts. The first 3 parts take up a chapter each, but then the 4th part is about sales and this takes up 4 chapters. The 5th part is about inheritance and takes up 2 chapters. The 6th part is dealt with in the last chapter.
2) At the beginning of the 9th Perek the Meiri writes that the Mishnah already started explaining about inheritance in Perek 8 and now in Perek 9 the elaboration of these matters are completed until their conclusion.
3) It seems that Perek 8 and Perek 9 are simply too long to be put in the Mishnayot as only one chapter. I saw in the Perush Darkei Noam on Pesachim that the last Perek of Pesachim has 415 words and is longer than the longest Perek in Masechet Shabbos. I have not checked this up. At any rate, it seems that a Perek of Mishnayos cannot be overly long and in fact if you look at Perek 8 and Perek 9 in Mishnayot Baba Basra they seem to be quite long [ I do not know if anyone is interested in counting how many words they contain]. BeKitzur they had to be split into 2 Perakim because otherwise they would simply be too long.
1) See also Midrash Rabah Vayikra 19:2 which tells us:-
"A fool says 'Who can ever learn all of the Torah; 30 chapters of Nezikin; 30 chapters of Keilim?!". But an astute person says 'I will learn 2 Halachot today, 2 Halachot tomorrow, until I have learnt all of the Torah".
2) We learn from this that there are 30 chapters in Nezikin. See Bava Kama end 102a that all of Nezikin is one Mashechta. In other words Bava Kama, Bava Metzia and Bava Basra are really all one Masechta. We now know that the 3 "Bavos" must contain 30 Perakim. It is logical to say that since we divide Nezikin into 3 smaller tractates, each of these must contain 10 chapters each. So Bava Basra must contain 10 chapters and therefore it would not be possible for Perek 8 and Perek 9 to be run together into one chapter because then Bava Basra would only contain 9 Perakim, so they have to be divided into 2.
1) Based on what we have seen it may be possible to suggest that the need to divide the Mishnayot into chapters, can explain even how two Masechtot can be divided up. Firstly, I should point out that it was Rabbi Yehudah Hanasi himself who instituted the division into Masechtot and Perakim. This is stated by the Rambam in his introduction to Seder Zeraim; DH veHaChelek HaShishi; where he writes that R. Yehuda Hanasi divided the Sedarim of the Mishnah into Masechtot, and then he divided the Mashechta into smaller units and called each one a Perek.
2) There is a well-known question; why does the first Mishnah in Bava Metzia discuss 2 people holding on to a Talit? This question is asked by the famous first Tosfos in Bava Metzia. Tosfos answers that it is because the last Mishnah in Bava Kama discusses who gets the wood shavings; is it the craftsman or the employer?, so the first Mishnah in Bava Metzia also discusses a dispute between 2 contestants for the ownership of a talit.
3) Until today, I had never thought of a different question; if the din concerning the dispute between the craftsman and the employer over the wood shavings, is so similar to the dispute over the talit, then why does the Mishnah say them in 2 different Masechtot? The Mishnah could have attached the contest over the talit to the end of the last Mishnah in Bava Kama, and Bava Metzia could have opened with the Mishnah that we now have on 9b about the person riding on a horse who saw a lost item?!
4) Based on what we have seen above I want to suggest that the 10th chapter in Bava Kama was too long already to attach the long Mishnah about the fight over the talit, and the follow-up about the 2 people riding on the animal. Therefore there was no choice but a new Masechta must divide between these 2 similar Mishnayot.
Dovid Bloom