THE CIRCULATION 



43 



Valves of the Heart. Located at suitable places in the 

 heart are four gate-like contrivances, called valves. The 

 purpose of these is to give the 

 blood a definite direction in its 

 movements. They consist of 

 tough, inelastic sheets of con- 

 nective tissue, and are so placed 

 that pressure on one side causes 

 them to come together and shut 

 up the passageway, while pres- 

 sure on the opposite side causes 

 them to open. A valve is found 

 at the opening of each auricle 



into the ventricle, and at the . Fir, 15. -Diagram showing 



plan of the heart, i. Semi- 

 opening of each ventricle into lunar valves. 2. Tricuspid valve. 



the artery with which it 

 connected. 



is 



rior vena cava. 10. Superior 

 venacava. II. Pulmonary artery. 

 12. Aorta. 13. Pulmonary veins. 



3. Mitral valve. 4. Right auri- 

 cle. 5. Left auricle. 6. Right 

 ventricle. 7. Left ventricle. 

 The Valve between the right 8. Chordae tendinese. 9. Infe- 



auricle and the right ventricle 

 is called the tricuspid valve. It 

 is suspended from a thin ring 

 of connective tissue which surrounds the opening, and 

 its free margins extend into the ventricle (Fig. 16). It 

 consists of three parts, as its name implies, which are 

 thrown together in closing the opening. Joined to the 

 free edges of this valve are many small, tendinous cords 

 which connect at their lower ends with muscular pillars in 

 the walls of the ventricle. These are known as the chorda 

 tendinea, or heart tendons. Their purpose is to serve as 

 valve stops, to prevent the valve from being thrown, by the 

 force of the blood stream, back into the auricle. 



The mitral, or bicuspid, valve is suspended around the 

 opening between the left auricle and the left ventricle, 



