CIRCULATION OF THE BLOOD. 



veins. It does not differ materially in its anatomy from the right. It is a little smaller, 

 and its walls are thicker, measuring about a line and a half. It has four openings by which 



it receives the blood from the 

 four pulmonary veins. These 

 openings are not provided with 

 valves. Like the right auricle, 

 it has a large opening, by which 

 blood flows into the left ven- 

 tricle. The arrangement of the 

 muscular fibres is essentially the 

 same as in the right auricle. In 

 adult life, the cavities of the au- 

 ricles are entirely distinct from 

 each other. Before birth, they 

 communicate by a large open- 

 ing, the foramen ovale, and the 

 orifice of the inferior vena cava 

 is provided with a membranous 

 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 disappears. 



The ventricles, in the human 

 subject and in warm-blooded 

 animals, constitute the bulk of 

 the heart. They have a ca- 

 pacity 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, and on the other, through the 

 entire system of the greater circulation to the right side. It has been asserted that the 

 capacity of the right ventricle is considerably greater than that of the left. The most 

 recent and conclusive observations on this subject are those of Hiffelsheim and Robin. 

 In these experiments, the cavities were filled with an injection of wax, and the estimates 

 were made by calculating the amount of liquid displaced by the moulds of the different 

 cavities. Care was taken to make the injection in animals before cadaveric rigidity had 

 set in, or after it had passed away, in the human subject. The comparative results ob- 

 tained by these observers are the most interesting, for the cavities were undoubtedly dis- 

 tended by the injection to their extreme capacity, and contained more than they ever 

 do during life. They found the capacity of the right auricle from one-tenth to one- 

 eighth greater than that of the left. The capacity of the right ventricle was from 

 one-tenth to one-eighth greater than that of the left, but more frequently there was less 

 disparity between the two ventricles than between the auricles. The capacity of each 

 ventricle exceeded that of the corresponding auricle by from one-fourth to one-third. 

 Nine times out of ten, this predominance of the ventricle >was more marked on the 

 left side. The absolute capacity of the left ventricle, according to these observations, 



FIG. 12. Heart, anterior view. (Bonamy and Beau.) 

 1, right ventricle; 2, left ventricle; 3, 4, right auricle; 5, 6, left auri- 

 cle ; 7, pulmonary artery ; 8, aorta ; 9, superior vena cava ; 10, ante- 

 rior coronary artery ; ll'branch of the coronary vein ; 12, 12, 12, lym- 

 phatic vessels. 



