Mark, here's some pictures, the second link is specific to your question I think:
http://www.spbrooks.com/join.htm http://www.spbrooks.com/pic251.htm A very simple joint that could easily be adapted to be fully housed (with bigger posts of course). Typically on the end post we run the mortise all the way through so that we have the entire thickness of the post through which to peg. We shoulder load carrying timbers and drop the spline low, the intersecting member then is rarely also load carrying, and in tension, so here we use a straight thru shorter spline. Usually the load carrying deeper spline is inserted first then the mortise redrilled and the intersecting spline run through, so that they are doing an over/under deal inside the post. Tight post to spline connection, glued and pegged. Voila!
