Chap. X] 



BLOOD VASCULAR SYSTEM 



165 



These cavities communicate with one another by means of 

 constricted openings, the auriculo-ventricular orifices, which are 

 strengthened by fibrous rings and protected by valves. 



Important orifices of the heart. — Eight large blood-vessels 

 are directly connected with the heart, hence there are eight orifices 



Ijcft pulmonary 



Left auricula 

 appeiiiliv 



__ Anterior coro- 

 nary vesselb 

 Dart pointing to 

 aortic opening 



Fig. 101. 



Left Auricle and Ventricle, the Hind Wall of Each having 

 BEEN Removed. (Gerrish.) 



plus the two between the auricles and ventricles, making a total of 

 ten. 



On the right side of the heart, the superior and inferior vena 

 cava empty into the auricle, and the pulmonary artery leaves the 

 ventricle. 



On the left side of the heart, four pulmonary veins empty into 

 the auricle, and the aorta leaves the ventricle. There are some 

 smaller openings to receive blood directly from the heart sub- 

 stance, and before birth there is an opening between the right and 



