How could I use the metamethods of other metatables?

Let's say I have table which, when parsed into a String, will return the name property of the table.

local Table_mt = { 
	__index = Table,
	__tostring = function(tab)
		return tab.name
	end
}

How could I make another table (with a separate metatable) use the __tostring() metamethod of this metatable, and add a touch of it's own? For example, it would return what Table's tostring method plus a number

local otherTable_mt= 
{ 
	__index = otherTable,
	__tostring = function(tab)
		return MYSTERY..tab.number; --MYSTERY is the call on the __tostring() of Table_mt
	end
}