RESPIRATION. 467 



The lymphatics of the lung are arranged in a superficial 

 and a deep set. The former ramify beneath the pleura, and 

 in the walls of the lobulettes; the latter accompany the 

 bronchial tubes and pulmonary vessels, to which they are 

 distributed. The two sets anastomose with each other, and 

 at the root of the lung unite, previous to their entering 

 the bronchial glands. These glands are situated in the 

 angle of bifurcation of the bronchi, as well as above and 

 around the primary bronchial tubes. In these glands the 

 lymphatic vessels terminate, and they in turn give rise to 

 different vessels, which, after passing through a number of 

 glands in the mediastinum, discharge their contents into the 

 thoracic duct. 



The nerves of the lung are derived from the sympathetic 

 and pneuniogastric. The latter nerves, on reaching the root 

 of the lung, divide into numerous branches, which join with 

 branches from the sympathetic to form two plexuses at the 

 root of each lung, one being above and one below the 

 bronchi. From these plexuses branches may be traced to 

 the bronchial glands, to the bronchial tubes nearly as 

 far as their extremities, to the larger blood-vessels, and, 

 according to Waters, to the pleurae and surface of the 

 lungs. 



MECHANISM or RESPIRATION. The movements of the 

 thorax by the respiratory muscles are the chief means 

 by which the actions of inspiration and expiration are 

 effected. The thorax is a conical cavity, with its apex 

 turned anteriorly, and its base posteriorly. The former 

 is closed by the trachea, oesophagus, several muscles, blood- 

 vessels, and nerves; the latter is entirely closed by ah 

 extensive muscular structure, the diaphragm. The sides 

 of the cone are formed above by the dorsal vertebrae, 

 below by the sternum or breast-bone, and laterally by 



