974 



THE ORGANS OF VOICE AND RESPIRATION. 



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

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



The posterior border is rounded and broad, and is received into the deep con- 

 cavity on either side of the spinal column. It is much longer than the anterior 

 border, and projects, below, into the phrenico-costal sinus. 



The anterior border is thin and sharp, overlaps the front of the pericardium, 

 and is projected into the costo-mediastinal sinus of the pleura. The anterior 



FIG. 538. Front view of the heart and lungs. 



border of the right lung is almost vertical ; that of the left presents, below, an 

 angular notch, the incisura cardiaca, into which the heart and pericardium are 

 received. 



Each lung is divided into two lobes, an upper and a lower, by a long and deep 

 fissure, which extends from the upper part of the posterior border of the organ 

 about three inches from its apex, downward and forward to the lower part of its 

 anterior border. This fissure penetrates nearly to the root. In the right lung the 

 upper lobe is partially subdivided by a second and shorter fissure, which extends 

 almost horizontally forward from the middle of the preceding to the anterior mar- 

 gin of the organ, marking off a small triangular portion, the middle lobe. 



The right lung is the larger and heavier ; it is broader than the left, owing to 

 the inclination of the heart to the left side ; it is also shorter by an inch, in conse- 

 quence of the Diaphragm rising higher on the right side to accommodate the liver. 



The Root of the Lungs. A little above the middle of the inner surface of each 

 lung, and nearer its posterior than its anterior border, is its root, by which the 

 lung is connected to the heart and the trachea. The root is formed by the bronchial 

 tube, the pulmonary artery, the pulmonary veins, the bronchial arteries and veins, 

 the pulmonary plexus of nerves, lymphatics, bronchial glands, and areolar tissue, all 

 of which are enclosed liy a reflection of the pleura. The root of the right lung lies 



