STRUCTURE OF THIRTY-THREE HOUR CHICKS 



73 



fore-gut the ventral aortic roots turning dorsad curve around 

 it, and then extend caudad, dorsal to the gut, as the paired 4 

 dorsal aortae (Figs. 23, 24 and Fig. 28, B). Few conspicuous 



ectoderm 

 of blastoderm 



head fold 

 of amnion 



prosen - 

 cephalon 



extra-embryonic 

 coelom 



tic mesoderm I lateral plate 



splanchnic mesoderm J ot mesoderm 



Fig. 28. — Diagrams of sections of 33-hour chick. The location of each section 

 is indicated on a small outline sketch of the entire embryo.'~" 



^branches arise from the aortae at this stage but as development 



>rogresses branches extend to the various parts of the embryo 



and the aortae become the main efferent conducting vessels of 



