THE KSOl'HAr.rS, STOMACH AM) INTKSTINE 



173 



The Intestine. In 5 mm. embryos (Fig. 177), the intestine, beginning 

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

 hepatic diverticulum and dorsal pancreas), and the cephalic and cauda 

 limbs of the intestinal loop, which bends ventrad and connects with the 

 yolk stalk. Caudally, the intestinal tube expands to form the cloaca. 

 It is supported from the dorsal body wall by the mesentery (Fig. 178). 



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 



Rathke's pouch 



\ 



Hypophysis (post, lobe) 

 Thyreoid 



Notochord 



Pericardium 



Allantois 



Dorsal pancreas 

 Ventral pancreas 



Cloacal membrane 



^ i i \ i^^^^f * 



Cacum 

 Urogenital sinus / ^-^U T JV^T'\ 



/ 1 \ Peritoneal cavity 



Tail gut \ Mesonephric duct 

 Rectum 



FIG. 179. Diagram, in median sagittal section, showing the digestive canal of a 9 mm. human 



embryo (adapted from Mall). X 9- 



(Fig. 179). At this stage the dorsal pancreatic anlage has been developed 

 from the duodenum, and, in the caudal limb of the intestinal loop, there 

 is formed an enlargement, due to a ventral bulging of the gut wall, that 

 marks the anlage of the ccecum and the boundary line between the large 

 and small intestine. 



Succeeding changes in the intestine consist: (i) in its torsion and 

 coiling, due to its rapid elongation, and (2) in the differentiation of its 

 several regions. As the gut elongates in 9 to 10 mm. embryos, the intes- 



