Polydactylous Horse

Polydactyl

 poly = multiple  dactyl = finger

Julius Ceasar's horse with multiple toes

An eight footed equine

Mark Sittich von Hohenems, Prince-Archbishop of Salzburg (1574-1619)

The horse had been obtained in Arabia, each of its alleged eight feet possessed its own horseshoe in the painting, and the painting itself is on public display at the Palace Helbrunn (now a museum), situated between Salzburg and Untersberg, Austria. 

Odin Rides to Hell on Sleipnir, an 8 legged horse.

Yes, it happens to people too!

What kind of bitting is this?

Here's the original photo followed by an enhanced close up.

I am familiar with overcheck bits. but this bitting looks unusual to me.

Tell me what's going on.

UPDATE: The best explanation received so far is that the large ring is a bit attached to the overcheck *and* the reins. Normally there is a separate overcheck bit but not always. The smaller ring on the side of the head is likely part of the caveson/noseband known as a race ing halter today and is used for cross tying the horse while harnessing etc and or for attaching other driving equipment to. There are what appear to be 2 reins on the near side (left). The bottom one likely is a lead for tying that is probably attached to the higher noseband ring on that side. 

Credit for this explanation goes to Lori Pennell and Dottie Billington and Janice Jones

It's a version of these bridles: