Medial Defects of the Cerebral Arteries of Some Mammals

IN 1930, defects were described1 in the muscle of the media of the cerebral arteries of man. They were found in the fork of bifurcations and lateral branchings. These defects have been considered by some to be the major etiological factor in the pathogenesis of intracranial aneurysms which occur so commonly in man and yet are rare in other animals. As I have been unable to find reference in the literature to any similar study in other species, an investigation was commenced in 1954 to confirm or deny their existence in the dog, horse and sheep. This communication is prompted by a comment in a recent book2 suggesting the advisability of such an investigation.