VIII.] THE BULBUS ARTERIOSUS. 261 



right chamber. This is caused by the canal from the 

 right ventricle into the bulbus arteriosus passing to- 

 wards the left, and on the ventral side, so as entirely 

 to conceal the origin of the canal from the left chamber 

 of the heart. On the seventh day the bulbus arteriosus 

 appears to come less markedly from the right side of 

 the heart. 



All these changes, however, of position of the bulbus 

 arteriosus only affect it externally; during the whole 

 time the two chambers of the heart open respectively 

 into the two divisions of the bulbus arteriosus. The 

 swelling of the bulbus is much less marked on the 

 seventh day than it was before. 



At the end of the sixth day, and even on the fifth 

 day (Figs. 84, 85), the appearance of the heart itself, 



FIG. 85. 



Iv 



HEART OF A CHICK UPON THE SIXTH DAY OF INCUBATION, 

 FROM THE VENTRAL SURFACE. 



La. left auricular appendage, r.a. right auricular appendage. 

 r.v. right ventricle, l.v. left ventricle, b. bulbus arteriosus. 



without reference to the vessels which come from it, 

 is not very dissimilar from that which it presents when 

 adult. 



