Shulchan Arukh, Yoreh De'ah 35

If the lung was punctured, the animal is invalid.

There are five minor lobes (definition: [parts that] are similar to ears) in the lungs, three to the right and two to the left when the animal is suspended by its feet and its innards are facing the butcher such that the right side of the animal and the right side of the butcher are the same. And there is one additional small lobe on the right side which is called the small roselike lobe and it doesn't stand in line [of the other] lobes, rather, it's distanced from them towards the front side. And if one is missing from the right or the left, or if there are two on the right and three on the left, the animal is invalid. Rema: The shapes of the right minor lobes are not similar to [the shapes] of the left [minor lobes], and if the shapes are switched, the animal is invalid. And so too, if the middle minor lobe on the right is larger than the one below it, the animal is invalid. And if the upper minor lobe on the left is larger than the upper minor lobe on the right, the animal is invalid. And so too, if the major lobe on the right is larger than [the major lobe] on the left, all of this is called switched, and the animal is invalid. And the roselike lobe, if it's missing, or if there are two of them or if it's found on the left side, it is valid. Rema: And in our countries the custom is to rule invalid whether two roselike lobes were found or if it was missing or if it's place was changed, and this should be the custom because there are great people who hold like this and one shouldn't change the custom. And so too, if its normal appearance or shape changes, the animal is invalid. If one found in it two roselike lobes that have a singular base, the thickness of a finger even though that they have a crack, it is valid. And if one is inverted and the second one is not inverted, we go after the one that's greater, and if it's not inverted it is valid. The [normal] way of the roselike lobe is to be in a pocket, and if it's not found in a pocket or if it has two pockets or if there is a pocket but [the roselike lobe] is not placed in it, and even if we would place the [roselike lobe] into [the pocket] it would return and go out from it when the lung inflates, the animal is invalid. And all of these laws are only [applicable] in places where the custom is to rule invalid an animal that has two roselike lobes or doesn't have a roselike lobe at all. But in places that [rule those cases] valid, also all of these distinctions are valid. If part of the roselike lobe is missing there is [reason] to check [for it] in the minor lobes or the major lobe on the left side. If the missing piece is found there are those that say it is valid because it is also found like this sometimes in goats and lambs. And so too there are those that rule valid if there is the appearance of a rose at its base, the thickness of a finger, even though there is no appearance of a rose at the head, as long as it is not inverted and has not changed its place. And in all of these things there is what to be lenient after many who rule valid in this entire topic.

If the number of lobes increased, if the extra lobe was on the side of the [other] lobes or in front of the lungs, which is on the side of the heart, it is permitted. And if it was on its back, which is on the side of the ribs, this is an invalid animal; and this is when it's [the size] of a myrtle leaf after it's inflated, but if it's less than that, it is valid. Rema: 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 validate an extra [lobe] on the front side, and one shouldn't change the custom.

If one finds an extra lobe at the end of the bottom edge of the major lobe, it is valid because this is called in the row of the lobes.

The right minor lobe which is close to the windpipe, in the narrow [part] of the chest, truly next to the neck, on the bottom which is the top that's next to the neck, if it is found on the back side like [the size of] a myrtle leaf, it is valid because it is its way to split. And this is precisely with the [lobe] on the right, but not [for the one] on the left. And there are those that say that this is precisely when it is in the upper half, but if it's in the lower half, it is invalid. Rema: ...