ROOT OF THE LUNGS. 521 



at such a distance from each other, and of such a figure, that 

 they allow the mediastinum and heart to intervene ; and they 

 cover every part of the heart anteriorly, except a small portion 

 at the apex. 



Each lung fills completely the cavity in which it is placed, 

 and every part of its external surface is in contact with some 

 part of the internal surface of the cavity ; but when in a natural 

 and healthy state, it is not connected with any part except the 

 lamina of the mediastinum. 



The lower extremity or base of each lung, rests upon the 

 pleural lining of the diaphragm, and fills up the angle between 

 the diaphragm and the ribs ; the superior end projects upwards and 

 backwards along the first rib and above the level of the clavi- 

 cle, so as to be separated from the scalenus anticus muscle only 

 by the pleura. In laborious respiration, the elevation of the 

 apex of the lung is increased, and the motion it produces 

 becomes visible at the root of the neck. The external face of 

 each lung is convex, to suit the contour of the thoracic parietes. 

 The internal surface, and especially that of the left, is concave to 

 accommodate the heart and pericardium. The anterior edge 

 is thin and sinuous, and presents on the left side a deep notch 

 fitted to the shape of the heart, and a sort of lobular projection 

 which in part covers that organ during deep inspiration. 



One great branch of the trachea and of the pulmonary 

 artery passes from the mediastinum to each lung, and enters 

 it at a place which is rather nearer to the upper rib than to the 

 diaphragm, and much nearer to the spine than the sternum : 

 at this place also the pulmonary veins return from the lungs to 

 the heart. 



These vessels are enclosed in a membrane, which is continued 

 over them from the mediastinum, and extended from then to the 

 lung. Thus covered they constitute what has been called the 

 Root of the Lung. 



When their covering, derived from the mediastinum, is 

 removed, the situation of these vessels appears to be such 

 that the bronchia are posterior, the branches of the pulmonary 

 44* 



