How to get access to the enclosing object of an inner class instance, from outside the class?

Here's an edited snippet of the code I'm working with:
abstract class Fragment { class Start extends Marker { def fragment: Fragment = Fragment.this } class End extends Marker { def fragment: Fragment = Fragment.this } }
When I first wrote this, I didn't put in the "def fragment" methods. But then I ran into the situation where I had a marker:
    val marker = aFragment.createStartMarker
and I realized I had no idea how to obtain a reference to 'aFragment' from 'marker'. I tried stuff along the lines of "marker.Fragment.this", but couldn't seem to find the magical invocation. So I defined the "fragment" methods to do the deed.
But I'd like to know how to get that reference without requiring an extra method to do it.
Thanks,Ken