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PERICARDIUM. 



Pericardium. The pericardium is a fibro-serous membrane like 



the dura mater, and resembles 

 Fig. 1 44.* that membrane in deriving its 



serous layer from the reflected 

 serous membrane of the viscus 

 which it encloses. It consists, 

 therefore, of two layers, an ex- 

 ternal fibrous and an internal 

 serous. The 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 dia- 

 phragm. The serous membrane 

 invests the heart with the com- 

 mencement of its great vessels, 

 and is then reflected upon the in- 

 ternal surface of the fibrous layer. 

 The heart is placed obliquely in the chest, the base being directed 

 upwards and backwards towards the right shoulder ; the apex for- 

 wards, and, to the left, points to the space between 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 princi- 

 pally by the right ventricle, and partly by the left. Surmounting 

 the ventricles are the corresponding auricles, whose auricular 

 appendages are directed forwards, and slightly overlap the root of 

 the pulmonary artery. The pulmonary artery is the large anterior 



* The anatomy of the heart. 1. The right auricle. 2. The entrance of the supe- 

 rior 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 tuberculum Loweri. 8. The musculi pec- 

 tinati in the appendix auriculae. 9. The auriculo- ventricular opening. 10. The cavity 

 of the right ventricle. 11. The tricuspid valve, attached by the chordae tendinse to the 

 carnetE 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 eavse, 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 pulmonnry veins. 18. The auriculo-ventricular opening. 

 19. The left ventricle. 20. The mitral valve, attached by its chordae tendineae to two 

 large columnse carnece, which project from the walls of the ventricle. 21. The com- 

 mencement 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 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-ventricular opening into the left ventricle, 

 whence it is conveyed by the aorta to every part of the body. 



