What bones did we find?

I went for a walk with my partner and we found a bunch of cool things while we were out, like Yellow Birch seeds, lots of White-tailed Deer scat, all sorts of neat lichens, and also a couple of bones, which based on their size were most likely from the White-tails.
The first bones I found were pretty interesting, quite a good length and size. It was also cool because it seemed like two bones fused together. I figured this would be a simple bone to figure out where it was from on this other animal, and I figured I should learn more about what purposes this bone supports.