Yosef Karo

“ And there are those who rule stringently and forbid all extra [lobes] that aren't in the row of lobes. And so too is the custom in some places to forbid an extra [lobe] even on the front side, and we don't differentiate whether it's on the front side or the back side. However, if [the extra lobe] stands in the row of lobes, and when it's inflated it leans toward the front side, it is valid. And if it leans toward the back side it is an invalid animal. And in our countries the custom is to rule valid an extra [lobe] on the front side, and one shouldn't change the custom. ”

“ All these things we check and measure after inflating the lung, because when the beast is alive the lung is inflated. Some say that with kids and lambs one would not declare the animal treifa if one did not find recognizable lobes, even without any distinguishing feature or split at all, for this is common, since in young animals there may be missing lobes and when they grow up the lobes develop. ”

“ But if there's a Sedek (crack, cleft, fissure) appearing to separate them, the size of a myrtle leaf, whether at their root, the middle, or end it's kosher.
Rema: And some declare it kosher by recognition or any hole even though it's less than a myrtle leaf (Rashi, Ittur, Tos., Samag, Rosh, Tur, R' Yerucham, Tashbatz, and Mordekhai כשם ה"ג ור"ח וש"ד וראבי"ה) , and we should rely on them in case of great loss and declare kosher. The lower lobe on the right, it's usually thicker and longer than the middle one, and also taller than that of the left. ”