268 Vertebrate Embryology 



The skeleton of the visceral arches. The de- 

 velopment of this part of the skeleton is also 

 very difficult to follow, and need only be men- 

 tioned, at this point, as it has already been dis- 

 cussed in connection with the fate of the visceral 

 clefts and folds. It will be remembered that 

 it was the jaws and the hyoid apparatus that 



FIG. 8 1. Two VIEWS OF THE HEART OF A CHICK ON THE FIFTH 

 DAY OF INCUBATION. (After Foster and Balfour.) 



A, from the ventral, B, from the dorsal side, /., left auricular appendage. 

 r.a, right auricular appendage, r.v^ right ventricle. /.z>, left ventricle. , bul- 

 bus arteriosus. 



were especially concerned in the development 

 of the visceral skeleton. It is the enormous 

 forward-growth of the jaws that is largely re- 

 sponsible for the characteristic outline to the 

 face of the chick. 



The heart. The fifth day is one of the 

 most important in the history of the devel- 

 opment of the heart. The most important 



