i8o 



THE ENTODERMAL CANAL AND ITS DERIVATIVES 



At 91 mm. the cardiac region shows a few longitudinal muscle fibers, which become distinct 

 in the pyloric region at 240 mm. 



The Intestine. In 5 mm. embryos (Fig. 171 A), the intestine, beginning at 

 the stomach, consists of the duodenum (from which are given off the hepatic 

 diverticulum and ventral pancreas), and the cephalic and caudal limbs of the 

 intestinal loop, which bends ventrad and connects with the yolk-stalk. Caudally 



Rathke's pocket 



Hypophysis 



Thyreoid 



Notochord 



Pericardium 



Allantois 



Dorsal pancreas 

 Ventral pancreas 



Cloacal membrane 



/\ i i \ ^^ma^^^f "* 



CcEcum 



Urogeniial simis I ^ -4 zz&?*^* ^ 



/ i ' \ Peritoneal cavity 



Tail-gut \ Mcsonephric duct 

 Rectum 



FIG. 172. Diagram in median sagittal section showing the digestive canal of a 9 mm. human embryo 



(adapted from Mall). 



the intestinal tube expands to form the cloaca. It is supported from the dorsal 

 body wall by the mesentery (Fig. 171 B). 



From 5 to 9 mm. the ventral bend of the intestinal loop becomes more marked 

 and the attachment of the yolk-stalk to it normally disappears (Fig. 172). 



The attachment of the yolk-stalk may persist in later stages (12 to 14 mm. embryos, 

 according to Keibel, Elze and Thyng). Also in 20 per cent, of adult intestines a pouch 3 to 9 

 cm. long is found where the yolk-stalk was formerly attached. This pouch, the diverticulum 

 of the ileum or MeckeVs diverticulum, is of clinical importance as many cases of intestinal occlu- 

 sion in infancy are due to its presence. 



