684 MANUAL OF PHYSIOLOGY. 



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

 folds, and the mesohlast 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 

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

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

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



FIG. 274. 



Longitudinal section of a foetal sheep. (Cadiat.) a. Pericardium. 6. Commencement 

 of diaphragm, c. Heart, d. Branchial arches, e. Pharynx. /. Origin of lung. g. Liver. 



and the descending colon ; whilst that part between the flexures 

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

 ascending colon. 



The csecum 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 inferior extremity of the caecum, which, owing to its feeble 

 growth, is of much smaller calibre than the upper part. 



