BLOOD VESSELS AND HEART CAVITIES 



185 



through the opening guarded by the tricuspid valve into 

 the right ventricle. This tricuspid valve is so constructed 

 as to open to admit the blood from the auricle when the 

 ventricle walls expand, and to prevent its flow backward 

 into the auricle when the ventricle contracts. It is in the 

 form of a curtainlike flap 

 which is fastened by chords 

 {chordm tendince) to raised 

 prominences on the ven- 

 tricle {papillary muscles). 



If we follow the seekers 

 from the right ventricle 

 they extend outward 

 through a single artery 

 known as the pulmonary 

 artery, since it conveys 

 blood from the ventricle 

 to the lungs. This artery 

 has at the base series 

 of valves or pockets of 

 a half-moon shape (semi- 

 lunar valves). These valves 

 are so arranged as to per- 

 mit the flow of blood 

 from the ventricle into 

 the artery when the ven- 

 tricle contracts, and pre- 

 vent its backward flow when the ventricle relaxes. 



The left side of the heart shows the following connec- 

 tions (see Fig. 69): Into the left auricle open four veins 

 (the right and left pulmonary veins) so-called because they 

 bring blood to the auricle from the right and left lungs. 



Fig. 69 — Left Bide of the heart (dis- 

 sected) ; 1, pulmonary veins ; 2, papil- 

 lary muscles ; 3, cut surface of the left 

 ventricle walls ; 4, semilunar valves at 

 the entrance to the aorta ; 5, pulmo- 

 nary artery ; 6, mitral valve ; 7, aorta ; 

 8, vena cava; 9, branches of the aorta. 



