312 



THE DEVELOPMENT OF THE CHICK 



onic intestine, we may next note a few details concerning some 

 of its divisions. The history of the mesenteries is considered in 

 Chapter XI). 



(Esophagus. Owing to the rapid elongation of the neck the 

 oesophagus quickly becomes a long tube. On the sixth day its 

 lumen becomes very narrow, and on the seventh day completely 

 occluded immediately behind the glottis, owing to proliferation 

 of the lining cells. On the eighth day the occluded portion 



Yen. jug. | 



1 



Mi 



O&s. 



Tr 



i 



Coptt 



FIG. 181. Photograph of a transverse section through the oesopha- 

 gus and trachea of an 8-day chick. 



Cop. H., Copula of the hyoid. (Es., (Esophagus. Tr., Trachea. 

 Ven. jug., Jugular vein. 



extends only a short distance behind the glottis: it is com- 

 pressed dorso-ventrally and extended laterally throughout the 

 occluded region (Fig. 181). On the eleventh day it is open again 

 along its entire length. The crop arises as a spindle-shaped dila- 

 tation of the oesophagus at the base of the neck; on the eighth 

 day it is about double the diameter of the parts immediately 



