LOBULES OF THE LUNGS. 801 



base of which is turned to the middle line (Fig. 13). The posterior 

 border of each lung, much longer than the anterior, is broad and 

 rounded, and occupies the deep groove on either side of the vertebral 

 column, reaching below, between the ribs and the diaphragm. 



Each lung is divided by a deep fissure, into an upper and lower lobe. 

 This principal fissure extends from the posterior border of the lung 

 near the apex, obliquely downwards and forwards, to the anterior 

 border near the base. The upper lobe, on each side, is smaller than 

 the lower one, and resembles a cone having an oblique base ; the lower 

 lobe has a somewhat quadrilateral shape. The upper lobe of the right 

 lung is subdivided by a second fissure, which, passing forwards and up- 

 wards from the oblique fissure to the anterior border, cuts off a small 

 triangular lobe, named the middle or third lobe of that lung. A rudi- 

 mentary third lobe is sometimes present in the left lung. In the right 

 lung there are sometimes four lobes. The right lung is about an inch 

 shorter than the left, and the concavity of its base is more pronounced : 

 this corresponds with the higher position and greater convexity of the 

 right half of the diaphragm, over the right lobe of the liver. The 

 right lung is also wider than the left, the breadth of the latter being 

 diminished by the projection of the heart into the left half of the 

 thorax. 



The root of each lung, which is found on the inner surface somewhat 

 above the middle, and much nearer the posterior than the anterior 

 border, contains, as already stated, the bronchus, the pulmonary ar- 

 tery, and the two pulmonary veins ; it also includes the nutrient ves- 

 sels or bronchial arteries and veins, lymphatics and lymphatic glands, 

 nerves, and areolar tissue, all being surrounded by a tubular reflection 

 of the pleura. In the root of the lung, the pulmonary artery is placed 

 behind the pulmonary veins, but in front of the bronchus, bronchial 

 vessels, and lymphatic glands. The relative position of the bronchus 

 and artery from above downwards, differs on the two sides ; on the 

 right side, the bronchus lies above the artery ; but on the left side, the 

 bronchus (Fig. Ill, 4), descending lower, to pass beneath the aortic 

 arch, is placed below the artery, 6. The pulmonary veins, 7, 8, on 

 both sides, are situated below the other structures. 



The air-tube, bloodvessels, lymphatics, and nerves, found in the 

 root of the lung, enter it, and, dividing and subdividing, penetrate not 

 only its lobes, but reach certain much smaller portions of the lung 

 substance, named the lobules. These lobules, which constitute the 

 proper pulmonary substance, or parenchyma, are small compressed 

 masses, which might be regarded as little independent lungs, or lung- 

 lets ; they fit accurately against each other; they vary in shape and 

 size, being, on the surface of the organ, large and pyramidal, with 

 their base directed outwards, whilst in the interior, they are small and 

 of irregular potyhedral shape. Each lobule is composed of a terminal 

 branch of an air-tube, surrounded by a cluster of air-cells communica- 

 ting with it; also of pulmonary and bronchial vessels, lymphatics, 

 and nerves, with a fine interstitial areolar tissue. The lobules are 

 supported on the terminal air-tubes, as if on stalks, but they are like- 

 wise held together by the vessels, and by an interlobular areolar tis- 



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