. Kirkes' handbook of physiology . pressure of the auricular systole. These currents aid in floatingthe valve leaflets into apposition. Thus, the auriculo-ventricular openingsare closed at the end of the auricular systole, , the end of the ventriculardiastole. The ventricular systole which follows simply serves to place the ACTION OF THE VALVES 157 valves under greater tension, thus closing them still more firmly. It shouldbe recollected that the diminution in the breadth of the base of the heart inits transverse diameters during the ventricular systole is especially markedin the neighborh
. Kirkes' handbook of physiology . pressure of the auricular systole. These currents aid in floatingthe valve leaflets into apposition. Thus, the auriculo-ventricular openingsare closed at the end of the auricular systole, , the end of the ventriculardiastole. The ventricular systole which follows simply serves to place the ACTION OF THE VALVES 157 valves under greater tension, thus closing them still more firmly. It shouldbe recollected that the diminution in the breadth of the base of the heart inits transverse diameters during the ventricular systole is especially markedin the neighborhood of the auriculo-ventricular rings, and this aids in render-ing the auriculo-ventricular valves competent to close the openings by greatlydiminishing the diameter. The cusps of the auriculo-ventricular valvesmeet not by their edges only, but by the opposed surfaces of their thin outerborders. The margins of the valves are still more secured in appositionwith one another by the simultaneous contraction of the muscular papillae,. Fig. 152.—The Tricuspid Valves of the Ox, Closed. Vertical section. (Krehl.) whose chordae tendineas have a special mode of attachment for this veryobject. They compensate for the shortening of the ventricular walls andthus prevent the valves from being everted into the auricle, an event thatdoes occur in certain valvular lesions. The actions of the tricuspid and mitral valves on the right and leftsides of the heart are essentially the same. The Semilunar Valves. The commencement of the ventricular systoleprecedes the opening of the semilunar valves by a fraction of a second. Theintraventricular pressure increases with the progress of the systole untilthere is a distinct increase over the arterial pressure, then the opening of thevalves takes place at once. They remain open as long as this differencecontinues. When the diastole of the ventricle begins and the arterial bloodpressure exceeds the intraventricular pressure, there is an initial reflux of
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