THE REGULATION OF THE BLOOD FLOW THROUGH THE HEART 165 



movements the directions of shortening, Haycraft found that the heart in its 

 natural position contracts in all its dimensions. 



According to Braun, in the shortening of the long axis of the heart during 

 systole its conical end becomes blunter and the long axis of the left ventricle 

 comes to form with that of the right a more acute angle than during diastole ; 

 at the same time the apex of the heart moves slightly to the right. 



Since the apex of the heart is its freest part, one would suppose that on 

 contraction of the long axis in ventricular systole the apex would approach 

 the base. But this is not the case : the base on the contrary approaches the 

 apex, and the heart as a whole makes no change in position. This phenomenon 

 appears to be explained partly at least by the recoil of the blood when it 

 rushes out through the arterial openings. That is to say, when the ventricles 

 drive the blood into the great arteries the apex is prevented by this recoil 

 from moving toward the base; and instead, presents a relatively fixed point 

 toward which the base is drawn (Chauveau and Faivre). 



The changes in form of the heart cavities have been studied only in heat 

 or in death rigor, where the contraction of the heart muscle has proceeded 

 much farther than it ever does in life. From such observations it appears 

 that even in these extremely contracted conditions the cavities of the heart 

 are never entirely obliterated. In the left ventricle an evident cavity remains 

 above the summits of the papillary muscles ; while the right ventricle is trans- 

 formed into a narrow slit, so that the two walls in the upper portion under- 

 neath the atrio-ventricular opening are still separated from each other by a 

 certain distance (Hesse, Worm-Muller and Sandborg; cf. Fig. 53). 



2. THE REGULATION OF THE BLOOD FLOW THROUGH THE 



HEART 



The normal course of the blood through the heart is determined chiefly 

 by its valves, but partly also by other means, which prevent the blood from 

 flowing in the wrong direction. 



A. THE ATRIO-VENTRICULAR VALVES 



Between the auricle and ventricle we have in the right heart the tricuspid 

 valve, in the left the mitral valve. 



The tricupsid is composed of a tubular membrane fastened around the entire 

 circumference to the atrio-ventricular ring. It is divided by deep incisions into 

 three large and one or two small flaps. These are attached by means of the 

 chordae tendinse to the papillary muscles or to the ventricular wall. The chordae 

 tendinse run partly to the free edge of the valvular flaps, partly to their ven- 

 tricular surface where they are attached broadly to the connective-tissue frame- 

 work of the flaps. 



The mitral valve is similar in all essential respects to the tricuspid, only it 

 is more firmly constructed in all its parts and consists of but two flaps. 



When the ventricles contract the blood is prevented by closure of the valves 

 from flowing back into the auricles, and is forced to take the right path into 



