. Text-book of anatomy and physiology for nurses. from auricle to ventricle is called ostium venosum. Endocardium.—The lining of the heart. It is thin and firm,resembling serous membrane in appearance, and is continuous withthe lining of the arteries and veins, thus making a perfectly smoothsurface throughout, for the current of blood. The Valves of the Heart, The valves of the heart are formed by folds of endocardiumstrengthened by fibrous tissue and placed at certain orifices of the different chambers—two inthe right heart and two inthe left. The opening be-tween the right auricle andventric
. Text-book of anatomy and physiology for nurses. from auricle to ventricle is called ostium venosum. Endocardium.—The lining of the heart. It is thin and firm,resembling serous membrane in appearance, and is continuous withthe lining of the arteries and veins, thus making a perfectly smoothsurface throughout, for the current of blood. The Valves of the Heart, The valves of the heart are formed by folds of endocardiumstrengthened by fibrous tissue and placed at certain orifices of the different chambers—two inthe right heart and two inthe left. The opening be-tween the right auricle andventricle (right ostium veno-sum) is guarded by the tri-cuspid valve, which is com-posed of three leaflets. Itallows the blood to flowdown into the ventricle butprevents it from flowingback. The opening betweenthe left auricle and ventricle(left ostium venosum) isguarded by the bicuspid (ormitral) valve, composed oftwo leaflets, allowing the blood to flow down into the ventricle butnot to return. (Both the tricuspid and mitral valves are connected. Fig. 115.—^Valves of the Right auriculo-ventricular orifice, dosedby the tricuspid valve. 2. Fibrinous ring. auriculo-ventricular orifice, closed by themitral valve. 4. Fibrous ring. 5. Aorticorifice and valves. 6. Pulmonic orifice andvalves. 7, 8, 9. Muscular fibers (auricles re-moved) (Bonamy and Beau.) VALVES OF THE HEART. l6l to certain muscle bands of the ventricles by tendinous cords whichcontrol the motion of the leaflets, preventing them from flying up-ward too far when the ventricles contract.) (Fig. 114.) The opening from the right ventricle into the artery which leavesit {pulmonary artery), is guarded by three semiluna rvalves, which arehalf-moon shaped pockets called the pulmonary valves. Likewisethe opening from the left ventricle into its artery {aorta) is guardedby three semilunar valves called the aortic valves (Fig. 115). The semilunar valves allow the blood to flow in one direction only—that is, awa
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