510 



THE BLOOD-VASCULAR SYSTEM 



toward the right. This margin is the margo acutus (fig. 423) ; it separates the 

 diaphragmatic surface from the sternocostal surface. The other margin of the 

 diaphragmatic surface is more rounded and shades gradually into the very wide 

 margo obtusus (fig. 423), which passes almost insensibly into the sternocostal 

 surface. The convex sternocostal surface [facies sternocostalis] (fig. 423), 

 directed forward and somewhat upward and to the right, is triangular and bounded 

 below by the margo acutus. To the left it goes over into the margo obtusus 

 along a line extending from the apex of the heart to the root of the pulmonary 

 artery. The margo obtusus corresponds to the rounded left side of the left 

 ventricle. 



The interventricular sulcus is a slightly marked groove indicating the separa- 

 tion of the ventricles upon the exterior of the heart. It lodges coronary blood- 

 vessels and a moderate quantitj^ of fat which can be seen through the epicardium. 



Fig. 424. — Base and Diaphragmatic Surface of the Heart. (After His.) 



Left pulmonary 

 artery 



Left superior pul- 

 monary vein 



Left inferior pul- 

 monary vein 



'Reflexion 

 of pericardium 



Coronary sinus 



Aorta 

 , Superior 



vena cava 

 . Right pulmonary 

 artery 



Right atrium 



Inferior 

 vena cava 





<s^-„- 



Margo obtusus 



f/. 



V 



Posterior longi- 

 tudinal sulcus 



Left ventricle 



^ 



Margo acutus 



The anterior part of this groove, sulcus longitudinalis anterior, beginning poste- 

 riorly, runs obliquely over the upper part of the margo obtusus on to the sterno- 

 costal surface. Crossing the margo acutus to the right of the apex, it is continuous 

 with the sulcus longitudinalis posterior upon the diai)hragmatic surface. The 

 diaphragmatic surface is formed about ecjually by the right and left ventricles, 

 and the sterno-costal surface mainly by the right. Where the longitudinal 

 sulcus crosses the margo acutus it produces a slight notch, the incisura (apicis) 

 cordis. 



The atria are separated (;xt(;rnally from the ventricles by the sulcus coronarius. 

 This is a horseshoe-shaped groove well marked below and laterally, and inter- 

 rupted above by the roots of the pulmonary artery and aorta. It lodges the 

 coronary sinus, smaller coronary vessels and fat. 



