GENERAL FORM AND POSITION. 



355 



therefore, has a very oblique position in the chest, and projects farther into the left 

 than into the right half of the cavity. Its position is affected to a certain extent 

 by that of the body ; thus it comes more into contact with the anterior wall of the 

 chest when the body is in the prone posture or is lying on the left side. In inspira- 

 tion, on the other hand, when the diaphragm sinks and the lungs expand, it recedes 

 slightly from the chest-wall. 



The heart is attached at its base to the great blood-vessels, and the serous layer 

 of the pericardium is here continued onto it. Otherwise the heart is entirely free 

 within the sac of the pericardium. The convex anterior surface looks somewhat 





leftpid? 

 -veins 



vena, actxseo 



Fig. 308. VIEW OF THE INJECTED HEART PROM BEHIND AND BELOW. (His.) f 



upwards as well as forwards towards the sternum and costal cartilages : from these 

 it is for the most part separated by the pleurae. The lungs also advance over it to 

 some extent, and encroach still farther during inspiration, so as in that condition to 

 leave only a triangular part, not more than two square inches in extent, uncovered. 1 

 The posterior or under surface is flattened, and rests on the diaphragm. Of the two 

 borders or margins formed by the meeting of the anterior and posterior surfaces, the 

 right or lower border, called margo acutus, is comparatively thin, and is longer than 

 the upper or left border, which is more rounded and named mar go obtusus. 



A deep transverse groove, the auricula-ventricular furrow, divides the heart into 



1 This uncovered part may be marked off on the surface of the chest by two lines drawn from the 

 point of the apex-beat to the middle line of the sternum, one horizontal, the other extending obliquely 

 upwards to between the fourth cartilages. 



VOL. II. 



A A 



