428 THE DYNAMICS OF CARDIAC ACTION. 



cavae or arterial blood from the lungs circulates in the Thebe- 

 sian system. 



Bochdalek found that many of these openings in the 

 auricles "presented the appearance of blind depressions, since 

 they were often covered with single valves in such a way as 

 to resist investigation with the blow-pipe" . . . "some 

 were slit-like, resembling the mouths of the ureters; still 

 others were large, round depressions, with smaller openings at 

 the bottom." The first remark suggests that the openings 

 serve as exits into the auricle, while the second points to the 

 contrary, since it is difficult to conceive of a depression with 

 "openings at the bottom" as a valve calculated to resist liquids 

 exerting pressure on the concave side. From the left auricle 

 Gad caused water to pass out of the right and left ventricular 

 walls, but, as the auricular openings have no valves, this only 

 serves to emphasize the extensive canalization which the 

 Thebesian system represents. The system might, therefore, 

 be considered as essentially calculated to distribute venous 

 blood from the right auricle to the entire heart: a fact which 

 the free anastomosis with the venous channels would seem to 

 sustain. 



Pratt states that he has seen "structures accessory to 

 these ventricular foramina which might in any way serve the 

 office of valves" . . . "the edge of the foramen is usually 

 sharply defined and may frequently exist as a partial, shelf- 

 like, covering, giving the impression perhaps of an attempt at 

 a membranous valve; but it is seldom more than this." A 

 shelf means a projection, and the fact that it is membranous 

 suggests that during ventricular contraction this valve is pressed 

 against the opening and closes it: a feature which involves 

 the possibility that during diastole a current whether venous 

 or arterial flows into the ventricle through its foramina. 

 That the latter and their valves open inwardly i.e., in the 

 ventricle is demonstrated by Pratt's experiment, in which he 

 injected the coronary veins with starch and celloidin and found 

 that even these passed into the ventricle. If, therefore, the 

 venous blood of the right heart at all enters the muscular 

 walls it is not through the foramina of the ventricle, i.e., from 

 below; it must be through the openings above, i.e., those in 



