The rete mirabile of the cranial base: a millenary legend.

The rete mirabile, a vascular network assumed to give origin to the intracranial segments of the internal carotid arteries, was interpreted by Galen as the key station for the conversion of the "vital spirit" into the "animal spirit." According to this interpretation, the rete was determinant either in sustaining the cerebral functions, or in controlling the reproductive process in humans. This belief was a firm point of the medical doctrine for centuries, accepted by the Islamic and Christian scholars of the Middle Ages. The new anatomy of Vesale, though having stated that the rete does not exist in humans, was unable to settle the discussion on its actual occurrence and function because it could not provide an alternative hypothesis on the mechanisms of support of the cerebral functions. Uncertainties still lasted in the late 17th century, when progress in knowledge on the circulation of blood and the minute anatomy marked the beginning of the new era in the medical science.