During the interval between contractions, the heart being in momentary repose, the blood pours into the auricles from the veins; the auriculo-ventricular orifices being widely open, the ventricles also receive blood; the auricles contract and the ventricles are filled; contraction of the ventricles follows; the auriculo-ventricular valves are forced up by the pressure of the blood and close the auriculo-ventricular openings and prevent the return of blood into the auricles; the contraction of the ventricles forces the blood from the right ventricle into the lungs through the pulmonary artery and its branches, and from the left ventricle into the aorta, thence through the arteries to all parts of the body.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
At the bottom of each auricle is the auriculo-ventricular opening, each provided with a valve to close it when the heart contracts to force the blood into the arteries.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
Above each true cord, and parallel with it, the ventricular fold or false cord is evident as a pink fold of mucous membrane.
"Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition."
Alexander Miles Alexis Thomson