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

Abstract

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.

Fig. 1

Intracranial carotid rete (CR) of a miniature Shiba goat injected vascularly with red latex. A paired arterial meshwork is formed at both sides and a single converged artery emerges from each rete (arrows) toward the brain. Dorsal view of the floor of the cranium with the dura mater removed. HF, hypophyseal fossa; OC, optic chiasm.

Fig. 2

Cervico-mandibular region of a lesser mouse deer in which the arterial vessels were injected with red latex. From the common carotid artery (CCA), a thinner internal carotid artery (IC) and a thick external carotid artery (EC) diverge. OA, occipital artery.

Fig. 3

Left and right internal carotid arteries (LIC and RIC) running rostrally on the floor of the cranium in a lesser mouse deer. After penetrating the dura mater, the artery diverges into rostral and caudal branches (RB and CB), which form the circle of Willis. No carotid rete is present. Dorsal view of the floor of the cranium with the dura mater removed. HF, hypophyseal fossa; OC, optic chiasm.

Fig. 4

Corrosion cast of arterial vessels in the brain of a lesser mouse deer. The internal carotid artery (IC) runs rostrally (left side) and diverges into rostral and caudal branches (RB and CB). In its course on the floor of the cranium, the internal carotid artery thins (arrowhead) and is surrounded by the cavernous sinus (CS).