The vessel bundle formed by the ramification of the median sacral was studied in 20 armadillos (Dasypus novemcinctus). This bundle, considered to be rete mirabile, is located in the sacral region close to the spine and to the base of the tail. The parallel arrangement of its arteries and veing gives origin to a countercurrent system that probably prevents heat dissipation through the end of the tail, thus participating in the control of body temperature in the armadillo