A comparative study of the extrinsic and intrinsic arterial blood supply to brains of submammalian vertebrates

The brains of submammalian vertebrates are supplied only by the paired internal carotid arteries each of which divides into a caudal and a rostral division. In fishes,where the necessities of existence are taken care of largely by the respiratory and taste centers in the brainstem augmented by olfaction, the caudal division is the larger. As locomotion becomes more important and complex in reptiles and birds, the corpus striatum and the cerebellum become larger, necessitating a gradual shift of arterial blood into the rostral division. At the reptilian level the cerebral branches have evolved sufficiently to be recognized as having a mammalianlike pattern, and it is at this point that the mammalian terminology can be applied. Branches of the basilar artery, which is formed by the union of the two caudal rami, retain their basically segmental arrangement. The vertebral artery has not yet appeared. The intrinsic vascular patterns are in the form of a wide‐meshed plexus, at first uniformly distributed among cells and fibers, but later more ldense in the nuclear areas. The first evidence of specialization in the vascular arrangement is the formation of a perineuronal plexus within the optic lobes in amphibians and in the appearance of a definitive striate artery. The vascular patterns are correlated with the phylogenetic development and the general functional development of members of each of the classes described.