From both the light and electron microscope observations of histological structure and mechanisms of contruction of arterial wall, the functional, formative mechanisms of elastic membrane of arterial wall may be explained as follows: The fundamental type of artery is the muscular-type artery in which the chain of smooth muscle cells runs criss-cross wise from left to right or vice versa in Archimedes spiral formation as viewed from the upper surface. That further differentiates and the chain disintegrates, resulting in individual smooth muscle cells bridging between the elastic membranes to form an elastic-type artery. In the case of the muscle-type artery of a relatively high differentiation, the smooth muscle cell chain is divided into equal parts each of which forms an individual Archimedes segment composed of original elastic components. In the case of elastic-type artery within such a segment, cells become individual smooth muscle cells. The elastic component ejected from the cytoplasm of each smooth muscle cell forms the elastic fiber sheath by its kinetic movement. This sheath in the muscle-type is divided into two equal numbers in the center of the above segment, and longitudinal sheath-segments of about one fourth of the original size separate to left and right, then at the horizontal level they form Archimedes segments with the original elastic networks by attaching themselves to the anterior-posterior surfaces and the lateral surface. However, only the inner layer of the internal elastic membrane is formed by the elastic prefibers of high ascending angle produced by endothel cells. In the case of elastic-type artery, the elastic sheath containing the individual smooth muscle cell is similarly divided into two equal parts at the center, which are further split up longitudinally that reinforce the original elastic network to form an elastic membrane. In each elastic sheath there are formed a spiral ascending fiber in the direction of the longitudinal axis and a fiber of approximately circular shape, the former of which becomes an ascending fiber and the latter becomes the longitudinal fiber of the elastic membrane. Therefore, the ascending angle of fiber of the elastic membrane is equal at the opposite surface of the stroma. In addition, the reason why the ascending angle of fiber is higher in the outer-layer fiber than in the inner-layer fiber is because the twisting phenomenon by contracting movement of the smooth muscle cells is stronger in those of the outer layer and the ascending angle of the fiber of elastic sheath is lower in the outer side.