Absence of carotid rete mirabile in small tropical ruminants: implications for the evolution of the arterial system in artiodactyls.

The intracranial carotid rete (or rete mirabile epidurale) is a unique blood vascular system supplying the brain of artiodactyls, which have either an involuted or no internal carotid artery. Although the lesser and greater mouse deer (Tragulus javanicus and T. napu, respectively) are ruminants, the rete mirabile epidurale is absent. In these animals, as in non-artiodactyls, such as canines, equines and humans, the complete internal carotid artery supplies the brain. It is currently uncertain whether the absence of the rete is confined to mouse deer among ruminants. The absence of the rete in mouse deer provides new insights into the evolution of the arterial system in artiodactyls.