72 PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



primitive auricle of the left twin has been divided in the ordinary 

 way, as is further evidenced by the presence of a well-marked foramen 

 ovale, and its left division has become the functional left auricle com- 

 mon to both twins. The primitive auricle of the right twin has not 

 been divided at all, or to be more accurate only the merest attempt 

 has been made at such division as is shown by the presence of a thin 

 strand, not unlike the moderator band, which is found crossing the 

 cavity of the functional right auricle. This undivided primitive auricle 

 of the right twin has been thrown into free communication with the 



(L.T.* 



Fig. 4. Diagram to illustrate the fusion of the two hearts in the region of the sinus venosus. 



right auricle of the left twin through the fusion in the region of the 

 sinus vinosus. Hence the functional right auricle common to both 

 twins represents what should have become the right and left auricles 

 of the right twin and the right auricle of the left twin. This is still 

 further borne out by the fact that three of the four auricular appen- 

 dages are connected with this functional right auricle. 



The fusion of the tubular heart of each embryo having occurred 

 in the region of the sinus venosus the ventricles have altogether 

 escaped, and hence the ventricles of the two twins are altogether 



