A comparative study of middle cerebral pressure in dogs and macaques.

1. A comparison has been made of the pressures recorded from pial branches of the middle cerebral artery in dogs and macaques. This pressure has been shown to be between 88 and 95% of femoral arterial pressure in dogs under chloralose anaesthesia, and between 80 and 90% of femoral arterial pressure in macaques similarly anaesthetized.2. The effect of occlusion of the main vessels in the neck is shown to differ considerably in the two species. Blood pressure within the forebrain of the dog is shown to be largely dependent upon the integrity of the external carotid artery, whereas in the monkey the external carotid artery is without effect in the maintenance of forebrain blood pressure. Occlusion of the four major arteries in the neck is shown to produce a greater effect in the macaque and to be accompanied by signs of medullary ischaemia in this species.3. After occlusion of the main middle cerebral artery, arterial pressure measured distal to the occlusion depends upon the integrity of collateral vessels from the other cerebral arteries. When only a branch of the middle cerebral artery is occluded, the greater part of the residual blood pressure depends upon anastomoses from other branches of the middle cerebral artery itself.