Fig. 1. Schematic representations of countercurrent heat exchangers in the appendages of a bottlenose dolphin. Cross-sections through (A) the dorsal fin, (B) the pectoral flipper and (C) the flukes. Inset below shows the positions of the cross-sections. Deep venous channels form peri-arterial venous retia (PAVR) surrounding central arteries (D). Superficial veins lie deep to the epidermis (thick black line) (modified from Pabst et al., 1999).