178 CIRCULATION. 



The left auricle receives the blood which comes from the 

 lungs by the pulmonary 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 pul- 

 monary veins. These openings are not provided with valves. 

 Like the right auricle, it has a large opening by which, the 

 blood flows into the left ventricle. The arrangement of the 

 muscular fibres is essentially the same as in the right auricle. 



In adult life the cavities of the auricles are entirely 

 distinct from each -other. Before birth they communicate 

 by a large opening, 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 this foramen 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 was supposed by Legallois 1 that the 

 capacity of the right ventricle was considerably greater than 

 the left, while the more recent observations of Bouillaud 2 on 

 the human heart seem to show that there is no great differ- 

 ence between the two sides in this regard. The most recent 

 and conclusive observations on this subject are those of Hif- 

 felsheim and Robin. 3 In these experiments the cavities 

 were filled with an injection of wax, and the estimates 



1 LEGALLOIS, (Euvrcs, Paris, 1824, tome i., p. 331. 



a J. BOUILLAUD, Traite Clinique des Maladies du Cceur, precede de Recherches 

 nouvelles sur VAvuitomie ct la Physiologic de cette Organc, Paris, 1841, tome i., p. 54. 

 3 Journal de V Anatomic et de la Physiologic, Paris, juillet, 1864, p. 413. 



