This refers to a person who has no known heirs: Eruvin 17a-b
This refers to a case where no one responds when the person who finds the body calls out: Eruvin 17a-b
Burying such a corpse wherever it is, regardless of ownership of the land: Eruvin 17a-b
What to do if the corpse is in a public plaza: Eruvin 17b
What to do if the corpse is in a plowed field: Eruvin 17b