The Caret Splitter sits opposite the (top of the) Triple Splitter. It is the small section of track which spans the end of the medium marble resting point which does not involve the Triple Splitter. I named it Caret Splitter because it is shaped like vaguely like a caret ^. It is actually shaped more like the Japanese character へ, when viewed from the direction the marbles will reach it.
The Caret Splitter
November 2018: The medium marbles work perfectly (~100% of the time), but the small marbles work 0% of the time. If the small marbles hit the left side, they fall willy nilly. If they hit the right side, they get stuck.