194 



1'lic Lungs 



gradually incline inwards behind the sterno-clavicular articulation, and 

 the manubrium, to the middle of the transverse ridge on the sternum ; 

 they then descend together as far as the fourth cartilage. From this 

 level the border of the right lung descends straight to the end of the 

 gladiolus, whilst the other slopes outwards in a line from the fourth left 

 cartilage to a spot two inches below and one inch internal to the left 

 nipple that is, to the apex of the heart thus leaving a triangular 

 surface of the right ventricle uncovered by lung ; the size of this super- 

 ficial cardiac region (p. 165) is, of course, in the inverse ratio of the size 

 of the lung, being large in phthisis, small or effaced in emphysema. 

 There is scarcely any lung-tissue behind the manubrium, the narrow 

 space between it and the spine being occupied by the trachea and 

 oesophagus and the large blood-vessels ; but, as the aorta is fixed to 

 the back of the chest by its intercostal branches, when the sternum 

 advances in inspiration the edges of the lungs must then glide inwards 

 towards the middle line. 



The root of the lung consists of the pulmonary veins, the pul- 

 monary artery, and the bronchus in that order from before backwards. 

 From above downwards the order is : on the left side, artery, bronchus, 

 veins, but on the right side the bronchus is higher than the artery, the 

 veins being still below and in front. The left bronchus descends to a 

 lower level than the right in its course beneath the aortic arch. The 

 root of the lung has pleura in front and behind, constituting the broad 

 ligament, between the folds of which are the bronchial vessels, sym- 

 pathetic and pneumogastric filaments, and lymphatics anti lymphatic 

 glands. 



Relations of the root of the lungr. On the right side, in front, 

 are the ascending aorta and the descending cava, the vena azygos 

 major (v. p. 185) arching over the root to end in the vena cava. 



On the left side the root lies in front of the oesophagus and the third 

 part of the aorta, and slopes beneath the aortic bend. Malignant 

 stricture of the oesophagus often occurs at the spot where it is crossed 

 by the left bronchus perhaps as the result of pressure. In front of 

 the left bronchus is the left auricle (v. p. 177). The phrenic nerve and 

 the anterior pulmonary plexus are in front of each root, and the vagus 

 and the posterior pulmonary plexus are behind. 



Infarction. The branches of the pulmonary artery pass in with 

 the bronchi and continue to divide until the ultimate capillaries enter 

 their respective lobules ; if a clot be dislodged from one of the 

 systemic veins say from an iliac vein, as after ' white leg ' and 

 be carried into the right heart and into a pulmonary artery, by acting 

 as a plug it throws out of work all that area of lung which the artery 

 supplied. This area will be wedge-shaped, with the apex at the site 

 of the plug, and the base at the surface of the lung ; in conformity to 

 the arborescent distribution of the vessels, the base must reach the 

 surface, for there the capillaries end. The larger the embolic clot (ei>, 



