Phylo- and -ontogenetically determined local changes in the structure of the arterial wall of vertebrates. Macroscopical findings.

It has been shown, by means of comparative anatomical, phylo- and -ontogenetic studies, that the focal structural changes occuring at seven points in the wall of the aortic arch and brachiocephalic arteries of reptiles, birds, and mammals, and in human-beinmnants of certain vessels which have regressed during embryonic development. They are considered to be loci minoris resistentiae and might therefore represent a site of predilection for pathological lesions, such as atherosclerosis. The existence of these "scars" in human-beings and birds has already been described. This paper presents definitive proof of their occurrence in reptiles (sea-turtle and crocodile) and mammals (dog, calf, sheep and monkey). It is therefore concluded that the "scars" in the aortic arch and brachiocephalic arteries are of phylogenetic origin.