174 



THE THIKU DAY. 



Fio. 60. 



[chap. 



Diagram of a poetion op the Digestive Tract op a 



Chick upon the Fourth Day. 



(Copied from Gotte.) 



The black inner line represents the hypoblast, the outer shading 

 the mesoblast. Ig. lung-diverticnlum with expanded termi- 

 nation, forming the primary lung-vesiole. St. stomach. 

 I. two hepatic diverticula with their terminations united by 

 cords of hypoblast cells, p. diverticulum of the pancreas 

 with the vesicular diverticula coming from it. 



the duodenum by the fact that from it, as vce shall 

 presently point out, the rudiments of the ducts of the 

 liver and pancreas are beginning to be formed. 



The posterior division of the digestive tract, cor- 

 responding to the great intestine and cloaca, is from 

 its very first formation nearly circular in section and 

 of a larger bore than the oesophagus. 



During part of the third day the hinder end of this 

 section of the gut is in communication with the neural 

 tube by the neurenteric canal already spoken of (Fig. 

 61, ne). The communication between the two tubes 



