An olive-sized piece of corpse [in a room] must have an opening of one hand-breadth and a [whole] corpse must have an opening of four handbreadths to prevent tumah from spreading to the [other] openings. But to allow tumah to spread, one [square] handbreadth [suffices]. [If it is] larger than the volume of an olive, it is treated as a [whole] corpse. R’ Yose says: A spinal column and skull are treated like a [whole] corpse.