Chapter 5, Mishnah 5. The mishnah continues dealing with buying cuts of meat from the butcher, and the question of what the buyer intends when he asks for a certain part of the animal. This mishnah is fully understood only by someone who lived in the time of the Mishnah and in the surrounding area where it was written, since it reflects the custom that was accepted there. To us, these things might seem a bit strange, but to a certain extent, this is true of all these mishnayos.
A Preliminary Distinction - Large and Small Livestock:
Kosher domesticated animals come in three types: cows, goats, and sheep. The cow is considered a "behemah gassah", meaning a large animal, while the goat and sheep are "behemah dakkah" (small animals) - a distinction known even from other contexts, such as the laws of tefillin and the like.
Regarding a large animal:
"Amar lo rosh behemah gassah - lo machar es haraglayim" - If one buys the head of a large animal from the butcher, he receives the head alone, since the head is an important cut of meat that stands on its own: the meat around the neck, the tongue, and similar parts. The legs are not included in the sale.
"Machar es haraglayim - lo machar es harosh" - And vice versa: the legs stand on their own, and the head does not come with them.
"Machar es hakaneh - lo machar es hakaved" - The "kaneh" is the trachea or windpipe (from the word for a plant reed or a pipe), which goes down to the animal's lungs. It is simple and clear that this sale includes the windpipe, the lungs, and the heart, to the point that the mishnah did not even need to mention it. The question is regarding the liver, which is the largest of the internal organs, and the mishnah establishes that the liver stands on its own and is not included.
"Machar es hakaved - lo machar es hakaneh" - And also the reverse: the windpipe, lungs, and heart are not connected to the liver and are not included in its sale. The two parts are separate from one another.
But regarding a small animal:
"Machar es harosh - machar es haraglayim" - One who buys the head of a sheep, a lamb (a young sheep), or a goat receives the legs together with the head.
"Machar es haraglayim - lo machar es harosh" - However, if one buys the legs, the head does not come with them, because of its special importance, and it is considered a separate purchase.
"Machar es hakaneh - machar es hakaved" - When buying the windpipe of a goat or sheep, the lungs and heart are included, and the liver is with them as well.
"Machar es hakaved - lo machar es hakaneh" - But if one makes a transaction to buy the liver alone, the windpipe, lungs, and heart do not come with it, and they are part of a separate purchase.
In summary: The mishnah establishes the parameters of a sale at the butcher according to the local custom in its time. For a large animal, each cut stands on its own: the head does not include the legs, the legs do not include the head, and the windpipe (with the lungs and heart) and the liver are separate from each other. For a small animal, the sale of the head includes the legs as well, and the sale of the windpipe includes the liver as well, but the sale of the legs does not include the head, and the sale of the liver does not include the windpipe.