THE LUNGS. 



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other contents of the mediastinum. Each lung is conical in shape, and presents 

 for examination an apex, a base, two borders, and two surfaces (Fig. 710). 



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FIG. 710. Front view of the heart and lungs. 



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. 



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. 



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 between the ribs and the Diaphragm. 



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

 cardium. 



Each lung is divided into two lobes, an upper and 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 

 from the middle of the preceding, forward and slightly upward, to the anterior 

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



