The Cerebral Blood Supply in the Giraffidae

Abstract

Summary. The course of the external carotid artery in the Giraffe and Okapi is described. Unfortunately, the Okapi was a defective specimen. In both there is a well‐developed carotid sinus with the usual innervation from the ninth and tenth cranial nerves. In the Giraffe only the external carotid runs into the rete mirabile caroticum. This has no connection with the vertebral artery, and blood can be shunted from it through the occipital artery and another vessel which is possibly homologous with the internal carotid, into the vertebral artery when the animal lowers its head. Both these short circuits arise together from the carotid sinus and presumably are controlled by reflexes from it. In the Okapi any connection between occipital and vertebral must be very small. The second connection with the carotid sinus is present, but this may not act a shunt since it was not possible to be certain that was no connections between the vertebral artery and the rete mirabile. The shunt mechanism would thus appear to be an adaptation to the presence of the excessively long neck in the Giraffe.