Physiology - A function for guttural pouches in the horse

Athletic animals must keep their brains cool during exertion because this organ can be damaged irreversibly by hyperthermia. But how horses do this has remained a mystery, as they don't appear to have thermoregulatory dervices like those found in other animals. They do, however, have a unique anatomical arrangement of their internal carotid arteries, which supply blood to the brain: these are enveloped by a pair of air-filled guttural pouches.

Here we show that horses use their guttural pouches to cool these important arteries during exercise, keeping the brain from overheating.