At risk of being a pedant, 2112's description is almost spot on - however, he has failed to mention a couple of other vital components in the Christen inverted system -
the air/oil seperator is what I think he is referring to when he says
a seperately mounted cannister which has some tube and ball bearing contraption inside
the oil valve is the clever bit of kit generally mounted on the firewall that works out correct direction of flow and egress for the breather
The other nifty devices are the T piece out of the top breather and the oil pick up strainers in the sump - one is very tall to help with knife edge oil pickup!
Stik