THE CIRCULATORY OR VASCULAR SYSTEM gi 



ventricle gives off the aorta, the largest arterial structure 

 in the body. The orifice of the aortic opening is guarded 

 by valves, called the semilunar; in the fetus two are 

 anterior and one posterior, but in the adult one is anterior 

 and two are posterior, right and left. 



FIG. 47. Left auricle and ventricle, opened and part of their walls re- 

 moved to show their cavities : i, Right pulmonary vein cut short j i', cavity 

 of left auricle; 3, 3', thick wall of left ventricle; 4, portion of the same 

 with papillary muscle attached; 5, the other papillary muscles; 6, 6', the 

 segments of the mitral valve ; 7, in aorta is placed over the semilunar 

 valves ; 8, pulmonary artery ; 10, aorta and its branches (Allen Thomson). 



Contraction of the ventricles takes place, at the same 

 time forcing the blood to the lungs from the right heart, 

 through the pulmonary artery, and to the body generally 

 from the left heart, through the aorta. 



The aorta, rising from the left ventricle, immediately 

 gives off, from its ascending portion, the two coronary 



