Oktzim, Chapter Two, Mishnah Three
1) If a pomegranate or melon has rotted in part, [what is rotten] does not join together.
2) And if [the fruit] is sound at either end but has rotted in the middle, [what is rotten] does not join together.
3) The stem of a pomegranate does join together, but the fibrous substance in it does not join together.
a) Rabbi Elazar says: also the comb is not susceptible to uncleanness.
Section one: The rotted part of the fruit does not join together to equal the requisite amount.
Section two: Even if both ends are okay and only the middle part is rotten, it still is not counted as part of the fruit.
Section three: The stem of the pomegranate is treated like other stems and it joins together with the fruit. But the little hairs inside the stem do not.
Albeck describes the “comb” as being a sort of “cup” around the fibrous substance whose edge looks like a comb. This part is cleanmeaning it doesn’t join together and according to the Tosefta it is not even considered part of the fruit such that it could be defiled.