968 



THE ORGANS OF DIGESTION. 



embryo and that part of it enclosed within is the pleuro-peritoneal cavity (Fig. 

 585). Finally, at the caudal end a hind-gut is formed and an anus added by a 

 process of imagination. 



Amnion 



Fore-gut / Heart 



Chorda Dorsalis 



FIG. 585. Diagram of a longitudinal section of a mammalian embryo. Very early. (After Quain.) 



Thus the whole alimentary canal was originally a straight tube placed in 

 front of the aorta, or the original two primary aortse, and that in front of the 



Fore-gut 



Mid-gut 



Hind-gut 



FIG. 586. Schematic median section of a human embryo. (After Dexter.) 



future vertebral column, the chorda dorsalis (Fig. 586). Along its middle 

 region, the anterior wall is lacking as it opens here into the yolk-sac. 



