134 HANDBOOK OF ANATOMY 



impressions of the organs against which it lies. The lower 

 border of the outer surface of the lung is thin and reaches 

 down between the diaphragm and the ribs to the level of the 

 lower border of the sixth rib in front; the eighth rib in the mid- 

 axillary line; then passes horizontally inwards, reaching the 

 vertebral column at the level of the tenth rib. The bases of the 

 lungs are in relation with some of the abdominal organs, the 

 diaphragm intervening. Thus, the base of the right lung rests 

 upon the right lobe of the liver, whilst the base of the left lung 

 is in relation with the left lobe of the liver, the fundus of the 

 stomach, and the spleen. 



On the anterior and lower part of the inner surface of each 

 lung is a deep recess made by the pericardium (this is deeper in 

 the left than the right) , and above the pericardial concavity is 

 the hilum of the luiig, where the bronchial vessels and nerves 

 enter, constituting the root of the lung. On the left lung, above 

 and behind the hilum is a broad shallow groove made by the 

 descending thoracic aorta. 



The left lung is divided into two lobes by a groove reaching 

 into the hilum ; it starts above on the outer surface just below 

 the apex and passes obliquely forwards and downwards to the 

 base near the middle line. The right lobe is divided by a 

 similar line into two, which, however, cuts the base nearer the 

 outer side. The inner and upper lobe is then subdivided by a 

 horizontal line passing inwards and forwards from about the 

 middle of the first line. 



The lungs entirely fill the thoracic cavity except for the space 

 in the middle occupied by the trachea, oesophagus, large vessels, 

 heart, and roots of the lungs. 



The Roots of the Lung's are formed by a number of structures 

 which pass into each lung at the hilum ; they consist of the pul- 

 monary veins, the pulmonary artery and the bronchus, nerves, 

 lymphatic vessels and glands. 



The Pleura is a serous membrane which invests the lungs and 

 lines the thoracic cavity. It is analogous to the peritoneum of 

 the abdomen, and performs the same function i.e., forms a 

 lubricated covering, so that the organs can move freely in the 

 cavity. The part lining the cavity is called the parietal pleura, 



