THE VENTRICLES 



177 



vena cava from the trunk and lower extremities. It also has a 

 transverse fold on the posterior wall called the Eustachian valve 

 or valve of the inferior vena cava, and a round depression on the 

 septum between the two auricles (atria), called the oval fossa (fossa 

 ovalis). The left auricle presents two large openings and several 

 small ones for veins, and communicates with the left ventricle. 



Posterior branch of 

 right coronary ar 

 tery 



Auricular appendage 

 Right coronary artery 



Preventricular branch 

 Right marginal branch 



Posterior interventicu- 

 lar branch of right 

 coronary artery 



r 



\M^< 



[RIGHT ^f 



^VENTRICIL'E 



Transverse branch of 

 right coronary artery 



Left coronary artery 



Anterior interventricu- 

 lar branch of left 

 coronary artery 



Left marginal branch 



FIG. 119. ANTERIOR SURFACE OF HEART. (Morris.) 

 The coronary arteries supply the substance of the heart. 



The ventricles expel blood from the heart. They include the 

 apex of the heart; their walls are thick and strong, the left one 

 being the thicker and larger of the two. Certain muscle-fibers in 

 the ventricles pass downward to wind around the apex of the heart 

 and then turn upward; others are transverse, still others oblique; 

 the arrangement causing the heart to harden in contraction, with a 

 twisting motion from right to left and a forcible pressure against 

 the chest wall. This is felt in the fifth interspace, at the left of the 

 sternum and is called the cardiac impulse. 



The muscle band of His (auriculo-ventricular bundle) is a name 

 given to a bundle of muscle fibers which connects the auricles and 

 ventricles; the contraction impulse is believed to travel from auricle 

 to ventricle by these fibers. 



12 



