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. 81. 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 



