THE LUNGS. 



717 



THE LUNGS. 



The Lungs are the essential organs of respiration ; they are two in number, 

 placed one in each of the lateral cavities of the chest, separated from each other 

 by the heart and other contents of the mediastinum. Each lung is conical in 

 shape, and presents for examination an apex, a base, two borders, and twc 

 surfaces. 



The apex forms a tapering cone, which extends into the root of the neck, about 

 an inch to an inch and a half above the level of the first rib. 



Fig. 365. Front View of the Thorax. The Ribs and Sternum are represented 

 in Relation to the Lungs, Heart, and other Internal Organs. 



The base is broad, concave, and rests upon the convex surface of the Dia- 

 phragm; its circumference is thin, and fits into the space between the lower ribs 

 and the costal attachment of the Diaphragm, extending lower down externally 

 and behind than in front. 



The external or thoracic surface is smooth, convex, of considerable extent, 

 and corresponds to the form of the cavity of the chest, being deeper behind than 

 in front. 



The inner surface is concave. It presents, in front, a depression corresponding 

 to the convex surface of the pericardium, and, behind, a deep fissure, the hilum 

 pulmonis, which gives attachment to the root of the lung. 



