What bone am I "cracking" in my chest?

Factual Questions
1

Every once in a while, I’ll inadvertently - never on purpose - crack something in my chest, much in the way that one might crack a knuckle or knee. It seems to be close to my sternum, somewhere in the top middle, and it usually cracks after I’ve been lying in a position I don’t normally assume - on my stomach for an extended period of time, or on my back in an unusual contortion while reading.

What’s going on? As far as I know, there aren’t any joints in the chest, nor are there even any connections where something like that might be happening. Isn’t that whole bone mass one solid piece?

Any ideas?

2

If your chest didn’t have any joints, you wouldn’t be able to breathe. The connections between your ribs and your sternum are flexible enough for that motion. If you look at the picture here, the dark areas are cartilage.

The sternum ossifies (turns to bone) from several different locations within the sternum itself. As you can see in some of the images here, some areas never fully join.

I get the same popping sounds in the same general area. I think it’s probably the cartilage that joins the ribs to the sternum that’s making the noise.