286 



THE DIGESTIVE SYSTEM 



(Fig. i). This connexion, which is termed the vitello- 

 intestinal duct, becomes relatively smaller, as the gut increases 

 in length, and it normally becomes obliterated entirely. It 

 may, however, persist, and the highest degree of persistence 

 consists in the presence at birth after the umbilical cord has 

 been divided of an umbilical fecal fistula. In the com- 

 monest variety, the proximal part of the duct remains as a 

 short blind diverticulum on the anti-mesenteric border of 

 the ileum about 3 feet from its termination. This variety of 



4 7 



I II. HI. 



FIG. 103. The Development of the Bladder and Rectum. 



In I., the cloacal membrane is just beginning to form. In II., it is very extensive, and 

 the cloaca is being divided into ventral and dorsal portions. In III., the sub-division 

 of the cloaca is complete and the uro-genital and anal membranes have ruptured. 



1. Hind-gut. 



2. Allantois. 



3. Cloacal membrane. 



4. Cloaca. 



5. Genital tubercle. 



6. Ventral, urinary, part of 



cloaca. 



7. Dorsal, gut, part of cloaca. 



8. Perineal orifice of uro- 



genital sinus. 



9. Anal orifice. 



persistent vitello-intestinal duct constitutes a Meckel's diverti- 

 culurn, and it is of importance because it may become adherent 

 to the mesentery and give rise to intestinal obstruction. 



The blind posterior part of the primitive alimentary canal 

 is known as the hind-gut. A sjnall diverticulum, termed the 

 allantois, passes from the ventral wall of the hind-gut, near 

 its cephalic extremity, into the body-stalk (Fig. 103). The 

 part of the hind-gut which lies caudal to the allantois is termed 

 the cloaca, and it subsequently becomes divided into a ventral 

 or urinary, and a dorsal or intestinal, segment. While this 



