616 



THE HEART. 



part, forming the base, and are termed auricles. The other 

 two occupy the middle and lower portions, constituting the 

 body and apex, and are called ventricles. 



198 - The right heart is com- 



posed of the right auricle 

 and right ventricle, (Fig. 

 199,) the left heart of a left 

 auricle and left ventricle, 

 (Fig. 200.) The right heart 

 receives venous blood ; the 

 left, arterial blood. 



We shall examine the 

 heart in the order of its 

 circulation. The blood en- 

 ters first the right auricle, 

 by the superior and inferior 

 vena cava ; from this cavity it passes into the right ventri- 

 cle, through the ostium venosum. From the right ventri- 

 cle it goes to the lungs, by the pulmonary artery. From 

 the lUngs it returns to the left heart by the four pulmonary 

 veins, entering at the left auricle. From the left auricle it 

 goes through the ostium arteriosum into the left ventricle ; 

 and from the left ventricle it passes out by the aorta, to be 

 distributed to all parts of the body. 



Eight Auricle. Make an incision from the superior to 

 the inferior cava, and cross it by another running trans- 

 versely along the centre of the cavity. On washing out 

 the blood there is seen, at the upper and posterior part, 

 the 'superior vena cava, descending obliquely forward and 



FIG. 198 represents the Cavities of the Heart, a Right auricle, b Superior 

 cava its entrance, c Inferior cava its entrance, d Entrance of coronary 

 vein, partly closed by valve, e Eustachian valve. / Fossa ovalis. g Tuber- 

 culum loweri. h Musculi pectinati. i Right auriculo-ventricular opening, 

 or ostium venosum. j Right ventricle, k Tricuspid valve. I Chordae-tendi- 

 neae, and carneae column, m Pulmonary artery its three semi-lunar valves, 

 seen at its commencement, n Right pulmonary artery, o Left pulmonary 

 artery, p Left auricle, q Openings of the four pulmonary veins, r Left 

 auriculo-ventricular opening, or ostium arteriosum. s Left ventricle, t Mi- 

 tral valve, it Aorta its commencement and semi-lunar valves, v Arch of 

 aorta. 



