Comparative anatomy was used to collect more evidence for a thermoregulatory function of the internal vertebral venous plexus (IVVP). The venous connections of the IVVP were studied and compared in various mammals in order to find evidence for the existence of climate related anatomical adaptations. Humans and vervet monkeys were chosen as representatives of mammals living in moderate climates, the IVVP of the dolphin was studied because this animal is always surrounded by cold water. The springbok was chosen as a representative of mammalian species living under very hot conditions. The present study was exclusively performed on post mortem material. After filling the venous system with latex the IVVP and its venous connections were dissected. It appeared that in the dolphin, veins from the trunk muscles were directly and exclusively connected to the IVVP in the absence of an azygos vein. In the vervet monkey and human specimens, veins originating in the muscles drained both into the caval veins and into the IVVP. In these mammals veins draining from brown fat areas were also connected to the IVVP. In the springbok, drainage of blood from the muscles was prevented to enter the IVVP by the presence of valves. In humans and vervet monkeys we found that the lumbar parts of the IVVP were connected to subcutaneous veins of the back. It was concluded that the anatomy of the IVVP and its connecting veins may serve to thermoregulate the spinal cord and that climate related anatomical adaptations were present in the species studied.
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