430 C. R. BARDEEN 



the umbilical cord (fgs. 4, 5, 6, 7). This part of the colon, to- 

 gether with the superior mesenteric artery, which runs nearly- 

 parallel with it, and the mesentery which is thickened along the 

 course of the artery, especially near the base, forms a stalk or 

 skeletal support from which the mesentery of the small intestine 

 seems to hang (fig. 7). The part of the mesentery of the free 

 small intestines attached to the part of the umbilical stalk which 

 extends or has extended into the umbilical cord may be looked 

 upon as belonging to coils which have developed within the 

 umbilical cord. The part of the mesentery of the free small 

 intestines attached to the abdominal part of the umbilical stalk 

 may be looked upon as belonging to the coils whichhave developed 

 within the abdominal cavity. 



The beginning of the development of the abdominal coils is 

 marked by the projection of a duodeno-jejunal loop to the left 

 beneath the umbilical stalk. In a 27 mm. embryo (fgs. 1, 2) 

 this loop extends to the left of the median plane and at its distal 

 extremity bends ventralwards (fig. 2). In a 35 mm. embryo this 

 duodeno-jejunal loop has begun to give rise to distinct jejunal 

 coils (figs. 3, 4). These coils now develop very rapidly so that in 

 a 40 mm. embryo they approximate in extent the ileac coils in 

 the umbilical cord (fgs. 5, 6, 7, coils on left side of umbilical 

 stalk). Just before the jejunal coils begin their most rapid de- 

 velopment the bursa omentalis becomes considerably distended 

 (figs. 2, 4). 



It is difficult to judge whether this distention is an active one 

 which helps to create more space in the abdominal cavity on the 

 left side, or a passive one due to a sudden increase in the space in 

 the left abdominal cavity. At this period the spinal axis of the 

 embryo in the lumbo-sacral region changes from ventral flexion to 

 dorsal flexion. Whatever factors may be involved in this the result 

 undoubtedly is to offer more space for intestinal development in 

 the abdominal cavity. The steps in this latter process are, first, 

 dilatation of the bursa omentalis; second, rapid development of 

 jejunal coils in the left abdominal cavity and a collapse of the 

 previously swollen bursa omentalis, and, third, the return to the 

 abdominal cavity of the ileac coils from the umbilical cord. The 



