This question is a follow-up to "Different-counts-of-the-248-organs-".
As we see from the Mishnah in Ohalot 1,8, only the bones are counted as organs, namely a bone that has a sinew and some flesh.
THe Gemmorah in Bekhorot 45 states that women have 252 organs (there are different opinions, however, based on different Torah verses that range from 251-253):
מעשה בתלמידיו של ר' ישמעאל ... שבדקו ומצאו בה מאתים וחמשים ושנים: אמר להם שמא באשה בדקתם שהוסיף לה הכתוב שני צירים ושני דלתות
(As the whole discussion is within the topic of impurity I imply that the count in Bekhorot applies to the bones also as in Ohalot.)
I couldn't find any empirical support for this claim, as anatomically, the two skeletons are identical (with 206 bones, not 248-252). Also, this seems to be a very easy anatomical test - counting bones - there shouldn't be any dispute at all.
Interestingly, if women had 4 additional bones, R"I's students could easily identify the female skeleton just by those 4 bones (2 axels and 2 doors?), not by the total number of 252! (thanks to DonielF)
So what is going on here with counting the female skeleton differently?