Комментарий к Эдуйот 1:7

רובע עצמות – one-quarter of a Kab of bones of the dead defile in a tent, and less [than one-quarter] do not defile other than through contact or by carrying [them] but not in a tent, but the School of Shammai holds that one-quarter kab defile and even if they are from many dead individuals.

Beth Shammai says: “A quarter-kav of any bones, even from two limbs or from three.”
And Beth Hillel says: “A quarter-kav of bones from a corpse, either from [the bones which form] the greater portion of the [body’s] build, or from the greater portion of the number [of the body’s bones].
Shammai says: “Even from a single bone.”
This mishnah begins to list disputes between Beth Shammai (the school of Shammai) and Beth Hillel (the school of Hillel). The rest of the chapter will contain disputes between these two schools.
Numbers 19:14 teaches that if a person dies in a tent things that are in the tent, including the people, can become impure, even though they have not touched the dead body. Our mishnah discusses how many bones must be in the tent for them to be considered a dead body which will cause ritual impurity.
According to Beth Shammai, a quarter-kav of bones will transmit impurity, as long as they come from at least two or three different bones. Beth Hillel agrees that a quarter-kav of bones is enough to cause impurity but they state that the bones must either come from the greater portion of the body (the hips, thighs, rib cage and spine) or from a majority of the number of bones in the body, considered to be 248. If there is a quarter-kav but they come from only one limb or many limbs but not a majority of the number or from the greater portion, they do not transmit impurity.
Shammai himself is even stricter than Beth Shammai, for he holds that a quarter-kav from one bone transmits impurity.

ובית הלל אומרים רובע עצמות מן הגויה – that is to say, from one body of one dead individual and not from may dead individuals. And even of one dead person, they do not defile until there will be one-quarter kab of the greater portion of a corpse, that is, the greater size of the body or the greater number of bones of a person which would be one-hundred and twenty-five bones, as the number of the bones of a person is two-hundred and forty-eight.

אפילו מעצם אחד – if one bone of the dead person files one-quarter kab, it defiles in a tent, and the Halakha is according to the School of Hillel.