428 C. R. BARDEEN 



The gastro-duodenal loop is simple and seldom shows funda- 

 mental variations, although individual differences in form in the 

 adult are frequent and well marked. Primitively it is of a simple 

 U form, as may be seen in figures 1, 3 and 5. Such variations as 

 are found in the adult seem to be due in the main to variations in 

 the position of the stomach and to variations in the development 

 of the entero-colic loop (for instance, see figs. 10 and 11). 



The left colic loop, although it begins its development consider- 

 ably later than the other two primitive loops (in fetuses 30-40 mm. 

 long, figs. 3, 4, 5, 6, 7) appears to be nearly as constant in forma- 

 tion. It is usually fixed at an early period in the vicinity of the 

 left side of the left kidney. From it develop the left half of the 

 transverse colon, the splenic flexure, the descending colon and the 

 sigmoid colon. Even in cases in which the entero-colic loop shows 

 marked abnormalities in development one usually finds the upper 

 part of the descending colon in approximately normal position 

 (see for instance, figs. 10 and 11). Aside from extremely terato- 

 logical cases and cases of complete situs transversus I have found 

 only one case clearly described in which the upper part of the 

 descending colon did not lie in the vicinity of the left kidney. 

 In this case, described by Koch,^ the colon extended in the mid- 

 dorsal line from the pelvis nearly to the transverse part of the 

 duodenum and then bent toward the right side. 



The relative constancy in the position of the upper part of the 

 descending colon is probably due to pressure exerted at an early 

 period by the neighboring intestinal coils against the mesocolon 

 of this portion of the gut (figs. 6 and 7). This part of the meso- 

 colon is thus caused to be fused against the dorsal wall of the 

 abdominal cavity. Proximal and distal to this region of attach- 

 ment of the colon variations in the development and disposition 

 of the colon arc frequent. 



Figures 8 and 9 exhibit somewhat extreme variations in the 

 development of the left colic loop above and below the region of 

 early fixation. Above this region the splenic flexure has sent out 

 a loop far to the right in front of the stomach, transverse colon 



1 Die angeborenen ungewohnlichen Lagen und Gestaltungen des menschlichen 

 Darmes, Deut. Zeitschr. f. Chirurgie, Bd. 50, s. 1, 1898. 



