Fifteen samples of human fetus aortic arch from induced abortion were prepared with routine scanning electron microscopic procedures. The samples were divided into 3 groups by fetus age and altogether 27 pictures were taken of them. By observing the internal elastic membrane on the samples where endothelial cells fell off, measuring the number of fenestrae and relevant area on the pictures with stereological method, and counting fenestra area per unit area. The result is that many small pores appeared on the internal elastic membrane of 2 month...
