The World Inside
The term “Centaurs” refers to a collection of hybrid races taking the form of the lower body of a quadriped and the upper body of a humanoid. The most common are the horse-based True Centaurs, though other varieties exist.
Centaurs, as is to be expected from creatures with such a strange construction, have equally strange biological traits. They are much stronger than other races their size because unlike others, they do not need to have intestines or other organs behind their humanoid abdomen – as such, their humanoid torso is more akin to a pillar of muscle and bone than the torso on an actual human.
The other most prominent difference in traditional biology is that centaurs have two pairs of lungs – each set is connected, however they also hook up to different respiratory orifices. The lungs in the humanoid torso, as expected, connect to the nostrils and mouth. The lungs in the non-humanoid torso, however, connect to a pair of vents at the front of the body – the dual lungs affords them remarkable speed, and allows them to support their unusually large bodies.