972 



THE ORGANS OF DIGPISTION. 



small intestines, and part of colon ; the inferior mesenteric, to the remainder of 

 the tube. 



The length of the intestine continually increases, and it becomes more bent 

 and tortuous, till from the third month on there occur two important changes, one 



FIG. 593. Torsion of the umbilical loop. Initial 

 position. (Jonnesco.) 



\Vitelline Duct 



FIG. 594. Torsion of the umbilical loop. Ac- 

 quired position. (Jonnesco.) 



in regard to a twist of the intestinal loop and one in regard to a change in posi- 

 tion of the stomach. The ascending and descending arms of the umbilical loop 

 have been lying side by side one above the other ; now the lower arm, which 

 becomes caecum and colon, begins to pass over the upper arm and crosses the small 

 intestine transversely (Fig. 598). The upper arm moves but little or none, as it 



Smatt in- 

 testine 



Vitettine 

 duct 



Greater curva- 

 ture 



Greater omen- 

 turn 



Place where the 

 intestines cross 



Large intestine 



Rectum 



Duodenum 



Appendix 

 Mesentery 



Vitelline 

 duct 



Greater 

 curvature 



Greater omen- 

 turn 



Placeuihere the 

 intestines cross 

 x 



Metocolon 

 Large intes- 

 tine 

 Small intestine 



Rectum 



FIG. 595. Development of human alimentary 

 canal and mesentery. Earlier stage. (Hertwig.) 



^a& 



FIG. 596. Development of human alimentary canal 

 and mesentery. Later stage. (Hertwig.) 



is already fixed to the vertebral column at its upper duodeno-jejunal end, perhaps 

 by the muscle of Treitz. 



The caecum, which has already developed an appendix, is thus landed wholly on 

 the right side of the body up under the liver (Figs. 594 and 596). At first there 

 is no ascending colon, the transverse colon running across the duodenum inferior 

 to the stomach and up to the spleen, making a splenic flexure ; it passes through 



