DEVELOPMENT OF THE INTESTINES 429 



and liver. Below this region the colon bends across the mid- 

 dorsal line to the right side of the body before descending into the 

 pelvic cavity. 



The entero-colic loop undergoes its early development in part 

 in the umbilical cord, in part in the abdominal cavity. The 

 umbilical part is finally withdrawn (in embryos about 40 mm. 

 long) into the right side of the abdominal cavity and subsequently 

 undergoes considerable shifting before the conditions character- 

 istic of the adult are reached. The more fundamental variation 

 in the development of this loop have to do first, with the intra- 

 umbilical and intra-abdominal development of the loop preced- 

 ing the withdrawal of the umbilical portion into the abdominal 

 cavity and, second, with the process of withdrawal of the umbilical 

 portion, the ultimate disposition of the various parts of the loop 

 within the abdominal cavity and their subsequent development. 



The development of the umbilical part of the loop has been 

 most carefully studied by Mall,- who has described the differenti- 

 ation of three primary coils of the small intestines within the umbil- 

 ical cord and their elaboration preceding withdrawal into the 

 abdominal cavity. This development is illustrated in figures 1. 

 2, 3 and 4 which correspond essentially with figures of correspond- 

 ing stages illustrated by Mall. There seems to be considerable 

 regularity in the early development of this part of the intestines. 

 Probably the conditions within the umbilical cord are fairly con- 

 stant and there is little there to interfere with free development. 



The active development of the entero-colic loop within the 

 abdominal cavity, on the other hand, seems to take place under 

 greater difficulties and to be subject to greater variation. It does 

 not begin until the development of coils within the imibilical cord 

 is well advanced and is relatively most active at the period im- 

 mediately preceding and during the return of the mnbilical coils 

 into the abdominal cavity. 



At this period the colon projects nearly straight forwards in 

 the median plane from near the lower border of the stomach into 



2 Ueber die Entwickelung des menschlichen Darmes und seiner Lage beim 

 Erwachsenen. His Archiv, 1897. 



