Here we'll talk about how the sale of slaughtered animals worked in the times of the Mishnah, what the custom was in terms of which parts of the animal they would sell, and what would be included in that package. The Mishnah says that somebody sells the head of a behemah gasah (large animal). In this case, it's talking about an animal like a bull or a cow. A behemah dakah, which is a small animal, is considered to be an animal like a sheep or a goat. So here he's selling the head of a large animal.
Lo machar et haraglayim. He hasn't included the legs of the animal together in that package with the head. The legs and the head of an animal are considered to be two main sections, separate from each other, and would be sold separately. Machar et haraglayim, lo machar et harosh. And the inverse as well: If he sold the legs of the animal, that would not include the head of the animal, because again, the head is its own section and is sold without the legs.
Machar et hakaneh, machar et hakaved. If somebody sold the windpipe of a large animal, the windpipe includes the lungs and the heart of an animal; he has not sold the liver with it. Machar et hakaved, lo machar et hakaneh. If he sold the liver of a large animal, he has not sold the windpipe of the animal as well. These, too, are considered significant and separate in this case, and therefore they are not included in the sale of each other.
Aval, badakah, but we're talking about a small animal, the halakha (Jewish law) becomes different. In small animals, certain sections are tiny and therefore are not considered to have any significance on their own, so they're thrown in with the sale of larger sections. Machar et harosh, lo machar et haraglayim. If he sold the head of an animal, included in the sale of the head of an animal, which is large, are the legs of an animal, which are smaller.
But machar et haraglayim, lo machar et harosh. If he sold the legs of an animal, which are small, the head of an animal is not included in that sale. In the case of a small animal, the head is considered significant, even when talking about a small animal, and it's sold on its own. Machar et hakaneh, machar et hakaved. If he sold the windpipe of an animal, the liver of that animal is included in that sale. Machar et hakaved, lo machar et hakaneh. But if he sold the liver, he has not sold the windpipe section of the animal; that's considered to be more significant.
So what we are saying here, basically, is that with small animals, if a small component of the animal was sold, the large components are not included in it. But if the large sections of the animal are sold, then some sort of small sections are included in that sale.