336 



SPLANCHNOLOGY. 



The small bronchial tubes, after ramifying in the lungs, terminate 

 in cellular recesses or air-cells, which consist only of the lining 

 membrane of the tubes. The muscular bands of the trachea are 

 continued along the inner face of the rings of the bronchi and 

 larger bronchial tubes, also gradually disappearing. These tubes 

 ai'e lined by mucous membrane, which is continuous with, but 

 more sensitive than that of the trachea. Blood is supplied by 

 the bronchial arteries. 



At the root of each lung there are a number of absorbent 

 bronchial glands. The principal ones are closely adherent to the 

 bifurcations of the bronchi. 



General view of the respiratory organs, a. Septum nasi ; h, Posterior naris ; c, Larynx ; d, Traclipa ; 

 c, Thyroid gland; //, Anterior mediastinum; g g, Posterior mediastinum; h, Left lung; h', Its 

 apex ; h". Its base ; h'", Its superior, and h"", Its inferior borders. 



THORAX. 



The thorax, or thoracic cavity, is formed by the ribs, sternum, 

 and bodies of the dorsal vertebrse, the intercostal muscles, 

 thoracic fascia, and diaphragm; it contains the lungs, the heart 

 and its adjuncts, the trachea, oesophagus, and a quantity of 

 nerves ; it resembles a hollow horizontal cone, flattened from side 

 to side. Its base, formed by the diaphragm, slopes obliquely 

 downwards and forwards. 



