CARDIAC VALVES 179 



smooth surface of endothelium throughout, for the current of blood 

 in heart and vessels. 



THE VALVES OF THE HEART 



The valves of the heart are formed by folds of endocardium 

 strengthened by fibrous tissue and attached to fibrous rings around 

 certain orifices of the different chambers two in the right heart 

 and two in the left. The opening between the right auricle and 

 ventricle, or tricuspid orifice, is guarded by the tricuspid valve, 

 which is composed of three leaflets. It allows the blood to flow 

 down into the ventricle but prevents it from flowing back. The 

 opening between the left auricle and ventricle, or mitral orifice, is 

 guarded by the bicuspid (or mitral) valve, composed of two leaflets, 



FIG. 121. VALVES OF THE HEART. 



i. Right auriculo-ventricular orifice, closed by the tricuspid valve. 2. Fibrous 

 ring. 3. Left auriculo-ventricular orifice, closed by the mitral valve. 4. Fibrous 

 ring. 5. Aortic orifice and valves. 6. Pulmonic orifice and valves. 7, 8, 9. 

 Muscular fibers (auricles removed). (Bonamy and Beau.} 



allowing the blood to flow down into the ventricle but not to 

 return. (Both the tricuspid and mitral valves are connected to 

 certain muscle bands of the ventricles by tendinous cords which 

 control the motion of the leaflets, preventing them from flying 

 upward too far when the ventricles contract.) (Fig. 120.) 



The opening from the right ventricle into the artery which 

 leaves it (pulmonary artery) , is guarded by three semilunar valves, 

 which are half-moon shaped pockets called the pulmonary valves. 

 Likewise the opening from the left ventricle into its artery (aorta) 

 is guarded by three semilunar valves called the aortic valves 

 (Fig. 121). 



