A rete mirabile (Latin for 'wonderful net'; plural retia mirabilia) is a complex of arteries and veins lying very close to each other, found in some vertebrates. The rete mirabile utilizes countercurrent blood flow within the net (blood flowing in opposite directions). It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient with respect to temperature, or concentration of gases or solutes. This term was coined by Galen.
Read more about Rete Mirabile: Effectiveness, Birds, Fish, Mammals