THE INTESTINAL CANAL. 687 



\".- The lower part of the fore-gut is of much smaller calibre than 

 the dilated portion forming the stomach ; it becomes the duode- 

 num, in connection with which arise two important viscera, the 

 liver and the pancreas. 



The mid-gut and hind-gut form the small and large intestines, 

 these being at first one straight tube, of which the small intestine 

 has the larger calibre. The small intestine, as it grows, falls into 



FIG. 275. 



Diagram of the alimentary canal of a chick at the fourth day. (Foster 

 and Balfour, after Gotte.) Ig. Diverticulum of one lung. St. Stomach. I. 

 liver, p. Pancreas. 



folds, and the mesoblast connecting it to the vertebral column 

 forms the mesentery. 



The large intestine is at first a straight tube lying to the left of 

 the embryo ; it becomes bent, and part of the tube is directed 

 towards the right side ; this develops another flexure, the portion 

 of intestine below which grows downwards. Thus that part re- 

 maining on the left side forms the rectum, the sigmoid flexure, 

 and the descending colon ; whilst that part between the flexures 

 becomes the transverse colon, and that on the right side the as- 

 cending colon. 



The caecum is developed from the ascending colon, the ileo-csecal 

 valve arising and shutting off the one part of the intestinal canal 

 from the other. The vermiform appendix originates from the 



