THE MEDIASTINUM. 



105 



Our chief interest in the mediastinum is naturally directed toward the heart, the methodical 

 examination of which in the living by percussion and auscultation is one of the most brilliant 

 and permanent results of the medical art. 



The study of the position of the heart should be preceded by a thorough study of the structure 

 of the organ. 



The Position of the Heart. For our purpose I will designate as the cardiac axis a line 

 drawn from the apex of the heart to the root of the aorta. Take an ordinary pointed lead-pen- 

 cil in the hand and assume that it represents the cardiac axis. Hold this "axis" vertically over 



Esophagus 



Arch of aorta with 

 left subclavian a. 



Superior lobe of left 

 lung 



Pulmonary artery 



Left coronary artery 



Pericardium 



Left auriculo-ventri- 



cular orifice 



Pericardial cavity 



Left ventricle 



Coronary sinus 



Diaphragm _. 



Esophagus 



Inferior vena cava 



Costo-mediaslinal 



sinus 



Stomach 



Descending aorta 



Right pleural cavity 



Superior lobe of left 

 lung 



Vena azygps major 



Point of bifurcation 



of trachea 



Right pulmonary 

 artery 



Central lobe of right 



lung 

 Left auricle 



Inferior lobe of left 

 lung 



-Diaphragm 



Hepatic vein in 

 "inferior vena cava 



Liver 



FIG. 49. A view of the dorsal surface of a frontal section of the thorax. 



the middle of the sternum with the apex downward, under the supposition that the right (venous) 

 heart is in the right half and the left (arterial) heart is in the left half of the body, and that the 

 intermediate septum is exactly in the median line. Now consider the four following points and 

 carry out the movements of the axis with the lead-pencil. 



1. The axis is not placed vertically, but obliquely, so that the apex (point of lead-pei 

 is directed to the left and the base (blunt end of lead-pencil) to the right. 



2. The axis, and consequently the entire heart, is pushed to the left, so that the i 

 plane of the body does not correspond to the median plane of the heart, but passes through tl 



