34: CIRCULATION OF THE BLOOD ACTION OF THE HEART. 



16 



branous fold, the Eustachian valve, which serves to direct the blood from the 

 lower part of the body through the opening into the left auricle. After 

 birth, the foramen ovale is closed and the Eustachian valve gradually disap- 

 pears. 



The ventricles, in the human subject and in warm-blooded animals, con- 

 stitute the bulk of the heart. They have a capacity somewhat greater than 

 that of the auricles and are provided with thick, muscular walls. It is by 

 the powerful action of this portion of the heart that the blood is forced, on 



the one hand, to the lungs and 

 back to the left side of the heart, 

 and on the other, through the en- 

 tire system of the greater circula- 

 tion, to the right side. 



The capacity of the cavities on 

 the right side of the heart is one- 

 tenth to one-eighth greater than 

 that of the corresponding cavities 

 on the left side. The capacity of 

 the ventricles exceeds that of the 

 auricles by one-fourth to one- third. 

 The absolute capacity of the left 

 ventricle, when distended to its 

 utmost (Robin and Hiffelsheim), 

 is 4-8 to 7 ounces (143 to 212 c. c.). 

 This is much greater than most 

 estimates, which place the capacity 

 of each of the various cavities, 

 moderately distended, at about two 

 ounces (59*1 c. c.) ; but the ob- 

 servations of Robin and Hiffel- 

 sheim, upon the human heart, 

 were made evidently with the 

 greatest accuracy, either before 



cadaveric rigidity had set in or 



left ventricular cavity ; 2, mitral valve ; 8, 4, colum- , , , ?. 



no? carneae, ; 5, aorf ic opening ; 6, aorta ; 7, 8, 9, alter it had disappeared. 

 aortic valves ; 10, right ventricular cavity ; 11, in- 

 terventricular septum ; 12, pulmonary artery ; 18, 

 14, pulmonjc valves ; 15, left auricular cavity : 16, 

 16, right pulmonary veins, with 17, 17, openings of 

 the veins ; 18, section of the coronary vein. 



Notwithstanding the disparity 

 in the extreme capacity of the va- 

 rious cavities, the quantity of blood 

 which enters these cavities is necessarily equal to that which is expelled. 

 This has been stated to be a little more than two ounces (about 60 c.c.). 

 There are, however, no means of estimating with exactness the quantity of 

 blood discharged with each ventricular contraction ; and the question seems 

 to be rather avoided in many works on physiology. Judging, however, from 

 observations on the heart during its action, it never seems to contain much 

 more than half the quantity in all its cavities that it does when fully dis- 

 tended by injection ; but the right cavities are more dilatable than the left 



