658 embryology: chick 



duct is formed by the folding in of the strip. Its end then grows 

 back under the peritoneum till it reaches the cloaca. 



Concerning the skeleton and muscles we shall not here add 



a.a. 



I, car. avit.v. 



v.c.a 



dC 



sv. 



v.c.p 



r vit.v. 



1 vitA. 



r.vit a 



p.vit.v 



l.vit.v. 



Fig. 514. — A diagram of the circulation of the chick at the end of the third day. 



The blastoderm is viewed from below. The arteries are black, the veins in outline. 



a.a., Second, third, and fourth arterial arches (the first has degenerated) ; a.vit.v., p.vit.v., veins from sinus 

 terminahs to left vitelline vein ; ao., dorsal aorta ; d.C, ductus Cuvieri ; e.car., i.car., external and 

 internal carotids ; l.vit.a., r.vit.a., left and right vitelline arteries ; l.vit.v., r.vit.v., left and right vitelline 

 veins ; s.t., sinus terminahs ; s.v., sinus venosus ; v., ventricle ; v.c.a., v.c.p., anterior and posterior 

 cardinal veins. 



The right anterior vitelline vein, which is not always present, has, if it existed, disappeared in the 

 dwindling of the right side of the system. 



anything to what has been said about the formation of these 

 organs in the frog (p. 641). 



BLOOD VESSELS 



Blood vessels arise during the latter half of the first day in 

 the loose mesoderm (mesenchyme) just above the endoderm of 



