Front Brakes - What are these for?

Forgive my ignorance but what are these 4 bolts for (circled in blue)? I noticed a few of these go straight through the caliper with nothing on the inside. They don't mount to anything.

 

Here is another angle (in blue)

 

When the calipers are orignally casted, it's done as 2 pieces (or in halves). Here's a photo that gives a clearer picture of that line running down the middle of the caliper; those 4 bolts hold the 2 pieces (of each caliper) together.




You can actually see the split in the caliper in your 2nd photo (top part of caliper).

 

Thanks! I didn't realize they were two pieces.