686 MANUAL OF PHYSIOLOGY. 



ductus vitello-intestiualis accordingly becomes obliterated, and 

 thus the raid-gut is closed at its lower aspect. 



The primitive intestine placed at the inferior aspect of the em- 

 bryo, just below the* protovertebrse, is lined internally by hypo- 

 blast, and covered externally by mesoblast. The cephalic or 

 anterior extremity of the canal is formed by uncleft mesoblast ; 

 the rest of the canal is formed by the splanchnopleural layer of 

 the mesoblast. 



A dilatation of a part of the fore-gut gives origin to the primi- 

 tive stomach ; this is quite straight at first, lying below the ver- 



FIG. 274. . 



Longitudinal section of a foetal sheep. (Cadiat.) a. Pericardium. 6. 

 Commencement of Diaphragm, c. Heart, d. Branchial arches, e. Phar- 

 ynx. /. Origin of lung. g. Liver. 



tebral column, with which it is connected by mesoblast. After 

 a time the stomach becomes turned to the right side, so that the 

 left surface of the organ comes to lie anteriorly and the right sur- 

 face posteriorly, the mesoblast connecting it with the vertebral 

 column, being developed into the peritoneal processes of the organ. 



