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. 8i. — 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 auricularappendage. 

 r.«, right auricular appendage, r.z', right ventricle. l.Vy 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 



