The circulus arteriosus cerebri in the guinea pig.

Arteries to the brains of guinea pigs were injected with latex and the circulus arteriosus cerebri was studied. Most of the arterial blood to the guinea pig brain came from the internal ophthalmic and vertebral arteries. The internal carotid arteries were extremely thin. In addition to an anastomosis that was found between the right vertebral and the basilar arteries in one specimen, the right vertebral artery anastomosed with the left vertebral artery in eight specimens and in one animal the basilar artery was double along a major part of its length.