476 



THE HEART. 



fibrous layer is attached, above, to the great vessels at the root of the 

 heart, where it is continuous with the thoracic fascia ; and below, to the 

 tendinous portion of the diaphragm. The serous membrane invests the 

 heart with the commencement of its great vessels, and is then reflected 

 upon the internal surface of the fibrous layer. 



Fig. 211.* The HEART is placed obliquely in 



the chest, the base being directed up- 

 wards and backwards towards the 

 right shoulder ; the apex forwards and 

 to fFe left, pointing to the space be- 

 tween the fifth and sixth ribs, at about 

 two or three inches from the sternum. 

 Its under side is flattened, and rests 

 upon the tendinous portion of the dia- 

 phragm ; its upper side is rounded and 

 convex, and formed principally by the 

 right ventricle, and partly by the left. 

 Surmounting the ventricles are the 

 corresponding auricles, whose auricu- 

 lar appendages are directed forwards, 

 and slightly overlap the root of the 

 pulmonary artery. The pulmonary 

 artery is the large anterior vessel at the root of the heart ; it crosses ob- 

 liquely the commencement of the aorta. The heart consists of two auri- 

 cles and two ventricles, w T hich are respectively named, from their position, 

 right and left. The right is the venous side of the heart ; it receives into 

 its auricle the venous blood from every part of the body, by the superior 

 and inferior cava and coronary vein. From the auricle the blood passes 

 into the ventricle, and from the ventricle through the pulmonary artery, to 

 the capillaries of the lungs. From these it is returned as arterial blood to 

 the left auricle ; from the left auricle it passes into the left ventricle ; and 



* 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 annulus ovalis. 7. The tubcrculum Loweri. 8. The musculi pecti- 

 nati in the appendix auricula. 9. The auriculo-ventricuiar opening. 10. The cavity 

 of the right ventricle. 11. The tricuspid valve, attached by the chordae tendineae 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 de 

 scending 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 in 

 ferior cavse, it passes through the auriculo-ventricuiar opening into the ventricle, and 

 thence through the pulmonary artery to the lungs. 10. The left auricle. 17. The open 

 ings of the fourth pulmonary veins. 18. The auriculo-ventricular opening. 19. The 

 left ventricle. 20. The mitral valve, attached by its chordae tendineae to two large co- 

 'umnae carneae, which project from the walls of the ventricle. 21. The commencement 

 nnd 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 pure 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-ventricuiar opening into the left ventricle, whence it is con 

 vyed by the aorta to every part of the body. 



