At the top, you can see the teeth that insert into the gears of the differential, and at the bottom, you can see the plate the bolts onto the end of the wheel/hub, which is what actually transfers the rotational power to the wheels, and also has the gasket to hold in the oil within the wheel assembly.

With the front wheels nearing completion (to be honest i'll be glad if I never see another spoke again!!) Ive moved to the front assembly. I'll be back to finish the front spokes on Monday.