THE MEDIASTINUM. 



107 



extent of this area of cardiac dulness. The projection of the entire heart upon the anterior 

 thoracic wall is also worthy of note. 



The projection of the heart upon the anterior thoracic wall is indicated by the following 

 lines upon the external surface: 



1. The inferior cardiac line commences in the fifth left intercostal space midway between 

 the mammary and parasternal lines (at the cardiac apex*), passes obliquely upward to the right, 

 and ends at the lower border of the fifth right costal cartilage, two centimeters from the sternal 

 margin. 



2. The right cardiac line commences at the termination of the inferior cardiac line, runs 

 directly upward at a distance of two centimeters from the sternal margin, and ends at the upper 

 border of the third right rib. 



Arch of vertebra -> 

 Sympathetic nerve 

 Azygos minor vein- 

 Inferior lobe of left 



lung 

 Descending aorta 



Esophagus- -- 

 Left vagus nerve 



Left auricle 



Superior lobe of left- 

 lung 



Left ventricle 



Root of the aorta 



Pericardium 

 Right ventricle - 



Sternum 



Latissimus dorsi 

 muscle 



Spinal cord 

 Azygos major vein 



XW-Bodv of vertebra 



- Serratus magnus m. 



Superior lobe of right 

 lung 



Pleural cavity 



Opening of superior 

 - vena cava in right 



auricle 

 .Superior lobe of right 



lung 

 -Right auricle 



Pectoralis major m. 

 Internal mammary 



artery 



Internal mammary 

 vein 



FIG. 50. A cross-section of the thorax at the level of the nipples. (The right lung is somewhat enlarged at the expense 



of the left one.) 



3. The superior cardiac line (not indicating any sharp cardiac boundary) commences at 

 the termination of the right cardiac line and runs to the middle of the second left intercostal 

 space, where it ends at a point three centimeters distant from the sternal margin. 



4. The lejt cardiac line commences at the termination of the superior cardiac line and runs 

 downward to. the cardiac apex. 



The transverse cardiac line should also be borne in mind; it commences where the i 

 cardiac line crosses the lower border of the sixth right costal cartilage and ends at the point of 



* The cardiac apex, as well as the apex-beat, is higher in children, sometimes being situated in the fourth intercostal 

 space; it is lower in the aged, where it may be found in the sixth intercostal space. 



