The aortic valve surrounds the orifice of the aorta and is formed by three semilunar cusps : two are anterior (right and left) and one posterior.
They are similar in structure, and in their mode of attachment, to the pulmonary semilunar valves, but are larger, thicker, and stronger; the lunulæ are more distinct, and the noduli or corpora Arantii thicker and more prominent. Opposite the valves the aorta presents slight dilatations, the aortic sinuses (sinuses of Valsalva), which are larger than those at the origin of the pulmonary artery.
The three cusps are formed by duplicatures of the lining membrane, strengthened by fibrous tissue.
They are attached, by their convex margins, to the wall of the artery, at its junction with the ventricle, their free borders being directed upward into the lumen of the vessel.
The free and attached margins of each are strengthened by tendinous fibers, and the former presents, at its middle, a thickened nodule (corpus Arantii). From this nodule tendinous fibers radiate through the segment to its attached margin, but are absent from two narrow crescentic portions, the lunulæ, placed one on either side of the nodule immediately adjoining the free margin.