THE INTESTINAL CANAL. 



685 



part of the alimentary canal. This hind-gut until the further de- 

 velopment of the bladder, etc., is in connection with the allantois 

 which arises as a bud from the lower part of the rudimentary 

 hind-gut. 



Between these two canals an intermediate one is formed by the 

 splanchnopleure of the mesoblast, which, at a distance from its 

 origin, becomes constricted, and shuts off an upper canal, the mid- 



FIQ. 273. 



Position of the various parts of the alimentary canal at different stages. 

 A. Embryo of five weeks ; B. Of eight weeks ; C. Of ten weeks. (Allen 

 Thomson.) /, Pharynx. *. Stomach, i. Small intestine, i 

 testine. g. Genital duct. u. Bladder, d. Cloaca, c. Crecum. 

 vitello intestinalis. si. Urogenital sinus, v. Yolk-sac. 



' Large in- 

 vi. Ductus 



gut, from a lower larger organ, the yolk-sac, the connection be- 

 tween the two forming the ductus mtello-intestinalis. 



Thus the primitive alimentary canal consists of an anterior and 

 a posterior canal, which are closed below, and a canal interme- 

 diate between these, which opens at its lower surface into the yolk- 

 sac. 



As the placental circulation becomes more and more developed, 

 so the yolk-sac shrinks and atrophies, until at last it is represented 

 by a fold of tissue connected with the primitive intestine. The 



