Despite the obvious existence of guttural pouches in Equidae, the question of their function has not yet been adequately answered. We suggest a working hypothesis that the guttural pouches of horses may be an additional organ of gas exchange. Research on the topographical location of the guttural pouches of horses and on the micro-morphological structures of their walls were carried out. It appears possible that: the dense arrangement of the vascular system of the wall of the guttural pouches near the main cerebral vessels; the constant moistening of the inner surface of the wall of the guttural pouches; and the air circulation in it; strongly suggests that the guttural pouches of horses may serve as an additional organ of gas exchange. The guttural pouches becomes very useful, particularly during prolonged periods of intense physical activity.
