Composition of encephalic arteries and origin of the basilar artery are different between vertebrates.

Intracranial arterial anatomy is lacking for most mammalian and non-mammalian model species, especially concerning the origin of the basilar artery (BA). Enhancing the knowledge of this anatomy can improve animal models and help understanding anatomical variations in humans. We have studied encephalic arteries in three different species of birds and eight different species of mammals using formalin-fixed brains injected with arterial red latex. Our results and literature analysis indicate that, for all vertebrates, the internal carotid artery (ICA) supplies the brain and divides into two branches: a cranial and a caudal branch. The difference between vertebrates lies in the caudal branch of the ICA. For non-mammalian, the caudal branch is the origin of the BA, and the vertebral artery (VA) is not involved in brain supply. For mammals, the VA supplies encephalic arteries in two different ways. In the first type of organization, mostly found in ungulates, the carotid rete mirabile supplies the encephalic arteries, the caudal branch is the origin of the BA, and the VA is indirectly involved in carotid rete mirabile blood supply. The second type of encephalic artery organization for mammals is the same as in humans. The caudal branch of the ICA serves as the posterior communicating artery, and the BA originates from both VAs. We believe that knowledge of comparative anatomy of encephalic arteries contributes to a better understanding of animal models applicable to surgical or radiological techniques. It improves the understanding of rare encephalic variations that may be present in humans.