368 



OF THE CIRCULATION OF BLOOD. 



Fig. 91. 



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; 5, 

 the Eustachian valve; 6, the fossa ovalis, surrounded by the annulis ovalis; 7, the tuberculum Loweri; 8, 

 the musculi pectinati in the appendix auriculae; 9, the auriculo-venlricular opening; 10,. the cavity of the 

 right ventricle; 11, the tricuspid valve, attached by the chorda? tendineEe to the carneae columnae (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 pulmonary 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 inferior 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 chordae tendineae to two large columnar carnerc. 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 dia- 

 gram. 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 conveyed by the aorta to every part of the body. 



of it into the ventricle. The blood, after having circulated through the lungs, 

 returns as Arterial blood, by the Pulmonary Veins, to the left Auricle ; whence 

 it passes through the mitral valves into the left Ventricle, and thence into the 

 Aorta, in the same manner with that on the other side, as just described. 



488. There are, however, some important differences in the structure and 

 functional actions of the two divisions of the Heart, which should be here 

 adverted to. The walls of the left Ventricle are considerably thicker than 

 those of the right; and its force of contraction is much greater. The follow- 

 ing are the comparative results of M. Bizot's recent measurements, taking the 

 average of males from 16 to 89 years. 



Base. Middle. Apex. 



Left Ventricle 4 lines 5*- lines 3| lines 



Right Ventricle 1 La lines If lines 1^- lines 



In the female, the average thickness is somewhat less. It will be seen that 

 the point of greatest thickness in the left Ventricle is near its middle ; while 

 in the right, it is nearer the base. The thickness of the former goes on 

 increasing during all periods of life, from youth to advanced age ; whilst that 

 of the righ| is nearly stationary. The left Auricle is somewhat thicker than 

 the right; the average thickness of the former being, according to Bouillaud, 



