ESOPHAGUS, STOMACH AND INTESTINE 



181 



At the stage shown in Fig. 172, the dorsal pancreatic anlage has been de- 

 veloped 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 which marks 

 the anlage of the ccecum and the boundary line between the large and small in- 

 testine. The caecal anlage later differentiates into the large ccecum and distal 

 vermiform process of the adult. 



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



Brain 



Tip of tongue 

 Thyreoid gland 



Pericardium 

 Gall-bladder 



Small intestine 

 Ccecum 



Hypophysis 



Foramen ccecum 

 Root of tongue 



Esophagus 



Trachea 

 Notochord 

 Spinal cord 



Liver 

 Stomach 



Urogenital sinus 

 Anal membrane 



Rectum 



FIG. 173. Diagrammatic median sagittal section of a 17 mm. human embryo showing the digestive canal 



(modified after Mall). 



to its rapid elongation and (2) in the differentiation of its different regions. As 

 the gut elongates in 9 to 10 mm. embryos the intestinal loop rotates. As a result, 

 its caudal limb lies at the left and cranial to its cephalic limb (Fig. 172). At 

 this stage the intestinal loop enters the ccelom of the umbilical cord. 



The small intestine soon lengthens rapidly and at 17 mm. (Fig. 173) forms 

 loops in the umbilical cord. Six primary loops occur and may be recognized in 

 the arrangement of the adult intestine (Mall, Bull. Johns Hopkins Hosp., vol. 9, 

 1898). In embryos of 42 mm. the intestine has returned from the umbilical 



