Since I see a lot of posts in the centaur tag wondering the various ways centaurs work, and since I work a lot of this stuff out in my head for my stories, worldbuilding/character design posts! This is gonna be a lot of pictures, so I’m breaking it up to give myself time to draw them. I’m not a doctor or a vet, so these aren’t completely anatomically accurate for humans or horses, it’s just to get a general idea of it.
Centaur skeletons are pretty similar to horse and human skeletons on their respective parts, the things I think people struggle with are 1) proportions, and 2) where they connect. I see a lot of right angles in the spine, which feels awkward and inflexible to me. I figured that since horses have vertebrae in their necks too, seeing how the horse neck connects to the shoulders could be a starting point for centaurs. Instead of pointing straight up, the spine works its way up in a more gradual S-curve. (An S-curve is closer to natural human posture than a straight line anyway.) It is more upright than how a horse would usually hold its neck, true, but the balance of it would also be different, since you don’t have that big heavy forward weight of the horse skull.
It’s interesting that some people seem to think a human torso would be heavier than a horse neck and head and this would require compensation, such as more muscular forelegs, heavier haunches, etc. There’s the rib cage and arms to consider, sure, but a human’s head is so much lighter than a horse’s, I feel like it would even out. A lot of human weight is in the legs and pelvis, which aren’t a factor here—centaurs only have one pelvis in the back, with the shoulderblades taking the place of hipbones in the front. Additionally, the weight is spread out differently, and there’s almost no weight in front of the forelegs unless they’re leaning forward, so that definitely doesn’t need additional weight to balance in the rear. If anything I worry that not having the weight in the front would throw their gait off in some way, but this is the point where fantasy biology is inherently ridiculous and you just gotta let stuff go.
My centaurs do have a pretty good range of flexibility, including being able to clean their rear hooves. The price for this is that there’s less room for organs in the human torso, but they do have the horse torso for most of their organ needs.
About the setting: this was originally part of a sort of homebrew Dungeons and Dragons thing, which took a lot of liberties with canon but was still noticeably derivative, but I went so far with the centaurs there’s pretty much nothing D&D about them, and as you will see in future installments, they’re just kinda weird even by centaur standards. I could break this off and make it its own thing without any difficulty, and I’ve considered doing that just to give it room to grow, but I also kinda like crossover appeal with my other stories/things, so for now it’s sort of nebulous setting-wise. I consider it part of my legendarium, which in the future will include fantasy biology, worldbuilding, religion, etc, for various monsters, beasts, and peoples, some of which is going to be very recognizably D&D, and some of which has drifted further. That’s kind of the nature of D&D though, it’s constantly being reimagined and reborn, and what you get in the manual is just the starting place.