2,546. The Lungs

Hilchos Shechita 6:21

An extra digestive organ only makes an animal a treifa either (a) when there’s a whole extra organ from start to finish, with the result that there are two such organs next to one another as sometimes happens in birds or (b) when the extra organ protrudes like a branch and it’s wholly separated, in either a bird or an animal. However, if the additional organ returns and recombines with the primary organ so that they’re joined at both ends, then even if they’re separate in the middle, the organ isn’t considered extra and the animal remains permitted.

Hilchos Shechita 7:1

There are two membranes on the lungs; if only one is punctured, the animal is permitted and if both are punctured, the animal’s a treifa. Even if the whole upper membrane peels off and disappears, the animal remains permitted. If there’s a hole of even the smallest size in the trachea in the chest or lower, the animal’s a treifa because this is a spot in the lower trachea that is unsuitable for shechitah.