CONTINUED interest in the neurosurgical treatment of congenital cerebral aneurysms of the circle of Willis and of vascular anomalies of the brain has stimulated an objective analysis of many aspects of the physiology of the cerebral circulation. Of these, an accurate evaluation of the adequacy of cross circulation in the circle of Willis is of primary importance to the neurosurgeon. There is abundant clinical evidence to show that disastrous tissue anoxia may ensue after ligation of the internal carotid artery in the neck or clip ligation of this same vessel within the cranium, if blood flow resistance across the circle of Willis is high.
The Matas test, initiated by digital compression of the internal carotid artery in the neck, customarily indicates gross inadequacies in hemispheral cross circulation, but a normal reaction to the Matas test does not guarantee freedom from cerebral complication secondary to anoxia. The concomitant use of an