Nachschlagewerk zu Oholot 2:11

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.”