Anatomical description of the vertebrobasilar and carotid systems forming the cerebral arterial circle in the equine brain.

Introduction: The cerebral blood supply in horses is maintained by carotid and vertebrobasilar systems, which join the cerebral arterial circle to ensure continuous brain perfusion. This study aimed to comprehensively describe the origins, courses, and interconnections of the vertebrobasilar and carotid systems in the horse brain. Methods: Ten adult equine specimens were obtained from horses euthanized for non-neurological reasons. Following perfusion with 10% formaldehyde, colored latex was injected into the arterial system, and detailed dissections were performed to study major intracranial vessels. Results: The vertebral and ventral spinal arteries merge to form the basilar artery, which courses rostrally along the ventral brainstem, giving rise to medullary, pontine, and cerebellar branches before joining the caudal communicating arteries. The carotid system enters the cranial cavity through the internal carotid arteries, which give rise to the rostral and middle cerebral arteries rostrally and the caudal communicating arteries caudally. Both systems form a complete cerebral arterial circle, ensuring extensive collateral circulation. Minor variations were noted in the origin and caliber of cerebellar arteries, and in the presence of a rostral communicating artery; however, the circle remained functionally intact in all specimens. Conclusion: These findings confirm that unlike ruminants, horses lack a carotid rete mirabile and retain patent internal carotids and a functional basilar artery, providing dual cerebral inflow that ensures vascular redundancy and stability, an adaptation for equine neurovascular physiology and comparative anatomy.