136 



STRUCTURE OF THE HEART. 



Diagram of single heart. 



Fig. 56. thus a double heart, or one of four cham- 



bers, arises. 



The diagram, Fig. 56, represents a 

 double-chambered heart, d being its auri- 

 cle, e the ventricle, c, <?, the veins converg- 

 ing to the auricle, a the aorta or main arte- 

 ry passing from the ventricle. The course 

 of the blood is indicated by the arrows. 



The heart with four cavities may be 

 considered as arising from the conjunction 

 of a pair of the preceding form, with their 

 efferent and afferent tubes, or arteries 

 and veins, so modified or arranged that 

 the right heart receives its blood from the 

 system in an auricle, from which it passes into a ventricle, and thence to 



the lungs. From the lungs, after aeration, 

 this blood is brought to the auricle of the 

 left heart, thence into its ventricle, and 

 thence to the aorta. Though all four cham- 

 bers are generally coalesced into one conic- 

 al form, the heart of the dugong, Fig. 57, 

 presents the true typical structure; E is 

 the right or pulmonary ventricle, L the left 

 or systemic ventricle, their apices being 

 quite apart ; D is the right or systemic au- 

 ricle, F the pulmonary artery, K the left or 

 Heart of the dugong. pulmonary auricle, and A the aorta. 



Fig. 58 is the anatomy of the human heart as viewed upon the right 



side, the figure and description being 

 from Dr. E. Wilson. 1, the cavity of 

 the right auricle ; 2, the appendix au- 

 ricuke ; 3, the superior vena cava, 

 opening into the upper part of the 

 right auricle; 4, inferior vena cava; 

 5, the fossa ovalis ; the prominent 

 ridge surrounding it is the annulus 

 ovalis; 6, the Eustachian valve; 7, the 

 o opening of the coronary vein ; 8, the 

 coronary valve ; 9, the entrance of the 

 auriculo- ventricular opening; a, the 

 right ventricle ; &, c, the cavity of the 



Human heart on the right side. right Ventricle, On the walls of which 



the columnce earner are seen ; c is placed in the channel leading upward 



