'0 



H. VON W. SCHULTE 



the heart tubes, which here are dilated. This enh^rgement rep- 

 resents the atrium. It is displaced well to the left of the median 

 line. This preliminary excursion in a direction opposite to that 

 occurring in later stages probably depends on the larger size of 

 the right omphalo-mesenteric vein and seems capable of play- 



Fig. 16 Reconstruction of the lumen of the heart in a cat embryo of sixteen 

 pairs of somites. Columbia Collection, No. 551. X 300. Reduced one-half. 

 /, Right bulb; 2, remnants of left bulb; 3, left ventricle; 4, right ventricle; 5, 

 interruption of right tube; 6, atrium; 7, left omphalo-mesenteric vein; 8, right 

 omphalo-mesenteric vein. 



ing a decisive role in determining the direction which the car- 

 diac loop will take. For the movement of the venous conflu- 

 ence to the left favors flow into the left ventricle as against the 

 right. This becoming engorged thrusts itself strongl}^ against 

 the shoulder of the left mantle, and the direction of the flow be- 



