SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 325 



924. EACH VENTRICLE HAS TWO OPENINGS, one 

 into and the other out of it, both situated at the upper 

 part of the ventricle, and both furnished with valves. 



925. THE VALVES AROUND THE OPENING INTO THE 

 VENTRICLE have an irregular, fringed edge, are con- 

 structed of sinewy tissue, and so arranged that when the 

 heart contracts, and the fibres attached to them relax, 

 the contents of the ventricle, crowding against the inner 

 surface of the valves, presses them together, and their 

 position being regulated by their muscles, the orifice 

 is closed. In the right, or pulmonary ventricle, the 

 valves having three main divisions are called tricuspid ; 

 in the left ventricle, the valves having two general divi- 

 sions are called bicuspid. 



926. THE VALVES AROUND THE OPENINGS FROM THE 

 HEARTS have a half-moon shape, and are called semilu- 

 nar, each one partially overlapping its fellow ; and at the 

 centre of each there is a little point, situated in such a 

 manner that, when the valves are down, the opening is 

 perfectly closed. 



927. THE USE OF THE VENTRICLES is to receive the 

 Blood from the auricles, and, by contraction, pour it out 

 into the arteries. 



928. Inf. The auricles and ventricles should not contract at the 

 same tune ; the auricles should first contract, and then the ventricles. 



929. THE AURICLES OF BOTH HEARTS CONTRACT at 

 the same time, occupying one fourth of the time of a full 

 contraction of the heart, thus resting three fourths of the 

 time. 



930. THE VENTRICLES OF BOTH HEARTS CONTRACT at 

 the same time, occupying one half the time, and resting 

 the remainder of a full beat. 



931. THE CONTRACTIONS OF THE HEART IN HEALTH, 

 AT MATURITY, are from 60 to 80 per minute, more fre- 

 quent in woman than in man, and in early than in late 



924. What has ? 925. Describe . 926. Describe . 92T. What is ? 928. Or- 

 der of heart's contraction. 929. How do ? 930. How do ? 931. What are ? 



