THE LUNGS. 493 



and by a membranous partition, the mediastinum. On the external or 

 thoracic side they are convex, and correspond with the form of the cavity 

 of the chest ; internally they are concave, to receive the convexity of the 

 heart. Superiorly they terminate in a tapering cone, which extends above 

 the level of the first rib, and inferiorly they are broad and concave, and 

 rest upon the convex surface of the diaphragm. Their posterior border 

 is rounded and broad, the anterior sharp, and marked by one or two deep 

 fissures, and the inferior border which surrounds the base is also sharp. 

 The colour of the lungs is pinkish-grey, mottled, and variously marked 

 with black. The surface is figured with irregularly polyhedral outlines, 

 which represent the lobules of the organ, and the area of each of these 

 polyhedral spaces is crossed by lighter lines. 



Each lung is divided into two lobes, by a long and deep fissure, which 

 extends from the posterior surface of the upper part of the organ, down- 

 wards and forwards to near the anterior angle of its base. In the right 

 lung the upper lobe is subdivided by a second fissure, which extends ob- 

 liquely forwards from the middle of the preceding to the anterior border 

 of the organ, and marks off a small triangular lobe. 



The right lung is larger than the left, in consequence of the inclination 

 of the heart to the left side. It is also shorter, from the great convexity 



* Anatomy of the heart and lungs. 1. The right ventricle; the vessels to the left of 

 the number are the middle coronary artery and veins ; and those to its right, the ante- 

 rior coronary artery and veins. 2. The left ventricle. 3. The right auricle. 4. The 

 left auricle. 5. The pulmonary artery. 6. The right pulmonary artery. 7. The left 

 pulmonary artery. 8. The remains of the ductus arteriosus. 9. The arch of the aorta. 

 10. The superior vena cava. 11. The arteria innominata, and in front of it the right 

 vena innominata. 12. The right subclavian vein, and, behind it, its corresponding ar- 

 teiy. 13. The right common carotid artery and vein. 14. The left vena innominata 

 15. The left caroti 1 artery and vein. 16. The left subclavian vein and artery. 17. The 

 trachea. 18. The right bronchus. 19. The left bronchus. 20, 20. The pulmonary 

 veins; 18, 20, form the root of the right lung; and 7, 19, 20, the root of the left. 21. 

 The superior lobe of the right lung. 22. Its middle lobe. 23. Its inferior lobe. 24 

 The superior lobe of the left lung. 25. Its inferior lobe. 



42 



