THE ORGANS OF THE INXER GERM-LAYER. 



297 



certain parts remain near the vertebral column, whereas others, 

 as a result of the folding, are more distant. The former are 

 attached by means of a narrow mesenter}^ and are consequently 

 less movable, the latter by their change in position have drawn 

 out their suspensorial band into a thin lamella, which sometimes 

 attains a remarkable breadth and allows a correspondingly increased 

 freedom of motion. 



The processes of development, 

 which are in part very complicated, 

 are satisfactorily explained by the ex- 

 cellent works of MECKEL, JOHANNES 

 MULLER, TOLDT, and His, even in 

 the case of human embryos, so that 

 these may serve as a foundation for 

 the description. 



In human embryos of the fifth 

 and sixth weeks the posterior sur- 

 face of the stomach, that which is 

 turned toward the vertebral column 

 (fig. 164 gc), is greatly distended; 

 the anterior wall (kc) on the con- 

 trary, which upon opening the 

 body-cavity is found to be covered 

 by the already voluminous liver, is 

 somewhat depressed. Consequently 

 a line running along the posterior 

 surface from the entrance of the 

 stomach (cardia) to its outlet 

 (pylorus) is much longer than the 

 corresponding line along the an- 

 terior surface. The latter becomes 

 the future lesser curvature (kc) ; 



the former, along which the mesogastrium is attached, is the greater 

 curvature (gc). 



The portion of the tube which follows the stomach has become 

 folded, in consequence of its great increase in length. From the 

 pylorus the intestinal tube (du) at first runs backward [dorsad] for 

 a short distance until it is close to the vertebral column, makes a 

 sharp bend here, and then describes a large loop, the convexity of 

 which is directed forward [ventrad] and downward [caudad] toward 

 the navel. The loop consists of two nearly parallel arms (d l and d 2 ) 



d 



Fig. 164. Diagrammatic representation 

 of the alimentary canal of a six-weeks 

 embryo of Man, after TOLDT. 



*/>, (Esophagus ; kc, lesser curvature ; 

 gc, greater curvature of the stomach ; 

 i/(', duodenum ; d 1 , part of the loop 

 that will become the small intestine ; 

 d z , pait of the loop that will become 

 the large intestine and begins with 

 the coecum ; d 3 , place of connection 

 with the vitelline duct ; 'ni(i, meso- 

 gastrium ; //, mesenterium ; m, 

 spleen ; p, pancreas ; r, rectum ; 

 (io, aorta ; d, cceliaca ; mei, mesen- 

 terica inferior ; ac, aorta caudalis. 



