Double aorta and dissecting aneurism. The upper and posterior wall of the aorta exhibited an opening one-fourth of an inch in diameter and nearly round. The aneurism had its origin in a rupture, not of the main artery, but in a channel to the left of it. It had stripped off the pleura on the left side and had broken through this, causing the fatal haemorrhage into that cavity. A careful examination showed that there was a duplication of the aorta from the left subclavian down, the two portions be ing separated by a complete septum. The right was the larger and was in line with the descending limb of the arch. The left branch did not exhibit arterio sclerosis.
This condition is very rare. Krause cited five examples of double aorta. In view of the fact that in the development of the human embryo the right and left systems of arterial arches fuse together at a very earlier period, it is astonishing that the man should have lived to a good age in health and comfort. Williams (Med. Record, Aug. 1, '961.
As to the etiology of dissecting anen risms, it is probable that neither trauma nor disease plays any part in the ma jority of instances. It is more than
likely that the initial tear in the inner coats is due to the distension of the lumen of the vessels in consequence of the increased action of an hypertrophied left ventricle. That the intim and media, and not the adventitia, should be torn is explained by the fact that the adventitious coat is more elastic than the other two. Flockmann (Mfinchener med. Woch., July 5, '9S).
Aneurisms are sometimes of parasitic origin and caused by embolism or by ero sion of the arterial wall from without, —ordinarily due to tuberculous foci as found in cavities in the lungs. Sponta neous aneurisms are common in patients with increased intravascular pressure, as in Bright's disease or valvular disease of the heart.
Every horse has an aneurism, from the size of a pigeon's egg to that of a man's head, in the mesenteric artery of the ewcum, caused by the selerostomum armatum. Czokor (Inter. klin. Rund., Nov. 26, '93).