Many involve stenosis of the atrioventricular valves or regurgitation of the semilunar valves. Many involve stenosis of the semilunar valves or regurgitation of the atrioventricular valves. The aortic valve is semilunar (half-moon shaped) with three cusps. The lunate bone (semilunar bone) is a carpal bone in the human hand. The thickenings are the origins of the three cusps of the semilunar valves. Blood is pumped from the heart, pushing open the pulmonary and aortic semilunar valves. The conus arteriosus has a variable number of semilunar valves. Two additional semilunar valves sit at the exit of each of the ventricles. These structures then open into the semilunar hiatus in the middle meatus. The semilunar valves close to prevent backflow into the heart. The lateral meniscus is also known as the external semilunar fibrocartilage. The closure of the semilunar valves causes the second heart sound. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. They are sometimes referred to as the semilunar ganglia or the solar ganglia. The sinus communicates through an opening into the semilunar hiatus on the lateral nasal wall.