Valvular structure at the branching portion of the human aorta

The Valvular structure developing at the site from which an artery was given off was examined. The valvular structure consisted mainly of smooth muscle cells, and was found at the openings of such small arteries as the intercostal and lumbar arteries. It was a crescent membrane-like structure extending from the peripheral edge of the opening to the downstream edge. This structure was indistinct in newborn infants, became gradually distinct in infants and stood out in teen-agers. It became rather thick and rounded in human beings more than 20 years of age. With further advance in age, the smooth muscle cells became degenerated and hyalinized with some disappearing eventually. In the valvular structure smooth muscle cells running longitudinally in the same direction as the blood stream were arranged in such a manner as a Venetion blind. This arrangement seemed to suggest that the valvular structure might have some function to adjust the blood stream at the branching portion of the aorta.