494 



EMBRYOLOGY OF THE CHICK 





pig. 

 pig. 



Fig. 291. 



Development of Digestive Tract. 



1 Transverse section of descending colon 10-mm. pig. 



2 Transverse section of descending colon 14-mm. pig. 

 Transverse section of descending colon 20-mm. 

 Transverse section of descending colon 25-mm. 

 Transverse section of descending colon 31-mm. pig. 

 Transverse section of descending colon 46-mm. pig. 



ABBREVIATIONS, 

 serosa. 

 undifferentiated middle layer. 



dm., dorsal mesentery. 



cm., inner circular smooth-muscle layer. 



lm., outer longitudinal smooth-muscle layer. 



mt., mesenteric taenia muscle band. 



sp., Meissner's plexus (submucous.) 



ap., Auerbach's plexus (intermuscular.) 



sm., serosa. 



subm., submucosa. 



p.m., primordial mucosae cells. 



N. B. Note especially rapid increase in 

 tube and the absolute decrease in thickness of mesenchymal wall 

 due to tension stresses elicited by the growth of the former. (Ebep 

 J. Carey in The Anatomical Record, Vol, 19. No. 4.) 



ridth of epithelial 



