Scala's '::' operator, how does it work?

In Scala, I can make a caseclass, case class Foo(x:Int), and then put it in a list like so:

List(Foo(42))

Now, nothing strange here. The following is strange to me. The operator :: is a function on a list, right? With any function with one argument in Scala, I can call it with infix notation. An example is 1 + 2 is a function (+) on the object Int. The class Foo I just defined does not have the :: operator, so how is the following possible?

Foo(40) :: List(Foo(2))

In Scala 2.8 RC1, I get the following output from the interactive prompt:

scala> case class Foo(x:Int)
defined class Foo

scala> Foo(40) :: List(Foo(2))
res2: List[Foo] = List(Foo(40), Foo(2))

I can go on and use it, but what is the explanation?