44 



THE VITAL PROCESSES 



-B 



with the free margins extending into the ventricle. It is 

 exactly similar in structure and arrangement to the tricus- 



pid valve, except that it is 

 stronger and is composed of 

 two parts instead of three. 



The right semilunar valve 

 is situated around the open- 

 ing of the right ventricle 

 into the pulmonary artery. 

 It consists of three pocket- 

 shaped strips of connective 

 tissue which hang loosely 

 from the walls when there 

 is no pressure from above ; 

 but upon receiving pressure, 

 the pockets fill and project 

 into the opening, closing it 

 completely (Fig. 16). The 

 left semilunar valve is 

 around the opening of the 

 left ventricle into the aorta, 

 and is similar in all respects to the right semilunar valve. 



Differences in the Parts of the Heart. Marked differ- 

 ences are found in the walls surrounding the different 

 cavities of the heart. The walls of the ventricles are much 

 thicker and stronger than those of the auricles, while the 

 walls of the left ventricle are two or three times thicker 

 than those of the right. A less marked but similar differ- 

 ence exists between the auricles and also between the 

 valves on the two sides of the heart. These differences 

 in structure are all accounted for by the work done by the 

 different portions of the heart. The greater the work, the 

 heavier the structures that perform the work. 



FIG. 1 6. Right side of heart 

 dissected to show cavities and valves. 

 B. Right semilunar valve. The tri- 

 cuspid valve and the chordse tendineae 

 shown in the ventricle. 



