ACTION OF THE HEART. 



551 



sound, and that of the second, are very closely allied ; and this view, which if 

 correct is of great importance in the explanation of numerous morbid phe- 

 nomena, harmonizes well with the known effect of a slight obstruction in a 

 tube, through which fluid is being rapidly forced, in producing a prolonged 

 sound, very analogous to the first sound of the heart. The following table 

 may assist the student in connecting the sounds of the Heart with its move- 

 ments. 



Ventricular Systole, and Auricular Diastole. Impulse of apex against 



parietes of chest. Pulsation in arteries. 

 First stage of Ventricular Diastole. 

 Short repose ; then Auricular Systole, and second stage of Ventricular 



Diastole. 



722. The course of the circulating fluid through the Heart, and the action 

 of its different valves, will now be briefly described. The Venous blood, 

 which is returned by the ascending and descending Vena Cava, enters the 

 right Auricle during its diastole ; and, when it contracts, is forced between 

 the Tricuspid valves, into the Ventricle. The reflux of blood into the veins, 

 during the auricular systole, is prevented by the valves with which they are 

 furnished ; but these valves are so formed, as not to close accurately, espe- 



[Fig. 212. 



FIRST SOUND. 



SECOND SOUND. 

 INTERVAL. 



The Anatomy of the Heart; 1, the right auricle; 2, the entrance of the superior vena cava; 3, the 

 entrance of the inferior cava ; 4, the opening of the coronary vein, half closed by the coronary valve j 

 5, the Eustachian valve ; 6, the fossa ovalis, surrounded by the annults ovalis ; 7, the tuberculum Low- 

 er! ; 8, the musculi pectinati in the appendix auriculae; 9, the auriculo- ventricular opening; 10, the 

 cavity of the right ventricle; 11, the tricuspid valve, attached by the chordae tendineae to the carnese 

 columnar (12); 13, the pulmonary artery, guarded at its commencement by three semilunar valves; 14, 

 the right pulmonary artery, passing beneath the arch and behind the ascending aorta; 15, the left pulmo- 

 nary artery, crossing in front of the descending aorta; *, the remains of the ductus arteriosus, acting as 

 a ligament between the pulmonary artery and arch of the aorta; the arrows mark the course of the 

 venous blood through the right side of the heart; entering the auricle by the superior and infeiior cava, 

 it passes through the auriculo- ventricular opening into the ventricle, and thence through the pulmonary 

 artery to the lungs ; 16, the left auricle ; 17, the openings of the four pulmonary veins ; 18, the auriculo- 

 ventricular opening ; 19, the left ventricle ; 20, the mitral valve, attached by its chorda? tendinea? to two 

 large columnar carneaj, which project from the walls of the ventricle; 21, the commencement and course 

 of the ascending aorta behind the pulmonary artery, marked by an arrow; the entrance of the vessel 

 is guarded by three semilunar valves ; 22, the arch of the aorta. The comparative thickness of the two 

 ventricles is shown in the diagram. The course of the arterial blood through the left side of the heart 

 is marked by arrows. The blood is brought from the lungs by the four pulmonary veins into the left 

 auricle, and passes through the auriculo-ventricular opening into the left ventricle, whence it is con- 

 veyed by the aorta to every part of the body.] 



