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: