Heart valve called the "semilunar valves". These two arteries receive blood from the ventricles and their semilunar valves permit blood to be forced into the arteries, and prevent backflow from the arteries into the ventricles. These valves do not have chordae tendineae, and are more similar to the valves in veins than they are to the atrioventricular valves. The closure of the semilunar valves causes the second heart sound. The aortic valve, which has three cusps, lies between the left ventricle and the aorta. During ventricular systole, pressure rises in the left ventricle and when it is greater than the pressure in
Lateral ventricles lateral, third, and fourth ventricles, connected by thinner channels. In the lateral ventricles, specialized areas – choroid plexuses – appear, which produce cerebrospinal fluid. If its production is bigger than reabsorption or its circulation is blocked – the enlargement of the ventricles may appear and cause a hydrocephalus. The neural canal that does not expand and remains the same at the level of the midbrain superior to the fourth ventricle forms the cerebral aqueduct. The fourth ventricle narrows at the obex (in the caudal medulla), to become the central canal of the spinal cord. Fetal lateral ventricles may be diagnosed