J. i. Bremer 467 
ventricle. This enormous right auricle is not, to my knowledge, figured 
im any model or drawing of human or other mammalian hearts of any 
stage, but conforms almost exactly to the Selachian heart. 
The blood enters the heart by way of the right auricle, from the sinus 
venosus, as is shown in Fig. 10. In this figure the heart is viewed from 
behind and slightly from the left side, and a portion of the model, the 
cee 
iew. 
dorsal wall of the sinus venosus, has been removed. The jugular veins 
from the head region and the umbilical veins from the body join on 
either side, on the left more anteriorly than on the right, and from this 
junction on each side an irregular sinus extends across the embryo, in- 
terrupted in places by bands of tissue (the cut end of one of which is 
seen in the figure) into which open dorsally the two vitelline veins. 
From this sinus venosus the blood passes to the right auricle by two sep- 
