DEVELOPMENT OF THE ALIMENTARY TRACT. 



1699 



r\ ^ 



FW-- 



into a descending and a transverse colon, the former being the upper part of the vertical 

 limb of the original dorsal flexure lying below the stomach. This flexure indicates 

 the division between the descending and transverse colon, since the latter corresponds 

 to the segment in front of the bend. Once back in the peritoneal cavity, the loops, 



which collectively lay in the sagittal 

 Fig. 1433. plane of the cord, are arranged gen- 



erally at right angles to the long axis 

 of the body, and the antero-posterior 

 colon becomes transverse ( MalP ) . In 

 consequence of these changes the por- 

 tion of the large gut that lay within the 

 cord now lies obliquely across the ab- 

 domen in front of the duodenum, the 

 remaining coils of the small intestine 

 being placed below. The caecum, 

 therefore, occupies a position beneath 

 the liver, on the right side, as a slight 

 dilatation at the beginning of the 

 transverse colon. The caecum, while 

 gradually increasing, retains this gen- 

 eral position until adjustment in the 

 length of the segments of the large 

 intestine takes place shortly after birth. 

 The lower part of the large gut is 

 thrown into a loop extending across 

 the abdominal cavity, which becomes the sigmoid flexure, the latter at birth including 

 nearly one-half of the entire length of the colon. After the fourth month after birch, 

 the sigmoid flexure becomes shorter and the other parts of the colon proportion- 

 ately longer, in consequence of which the caecum is pushed downward towards the 

 right iliac fossa, with corresponding lengthening of the ascending colon. These por- 

 tions of the large intestine, however, continue to grow for some time after birth, 

 and it is not until the third year that they acquire their definitive relations. 



The anomalous arrangement and position of the transverse and ascending colon 

 and the caecum, not infrequently observed in the adult, are usually dependent upon 

 arrested de\^elopment, the large intestine failing to take up a transverse and superior 

 location, and hence altering its relations with the small intestine. 



Reconstruction of intestinal tube and part of liver of 

 human embryo of 17 mm. vertex-breech length. (Same em- 

 bryo as represented in Fig. 1436.) //^', hepatic vein; ri\ 

 umbilical vein; PI', portal vein; GB, gall-bladder; PIV, 

 foramen of Winslow. The figures in this and in the two 

 following reconstructions refer to corresponding parts of the 

 gut-tube, I being gastro-duodenal junction. \"i2. (Mall.) 



Fig. 1434. 



Fig. 1435- 



Reconstruction of intestinal coils of human embrj'o 

 ot 28 mm. vertex-breech length. Arrow indicates po- 

 sition of foramen of Winslow. X 8. (Mall.) 



Reconstruction of intestinal coils of human embryo oi 

 80 mm. vertex-breech length. X 2. (Mall.) 



The caecum, which first appears as a slight lateral diverticulum from the larger 

 inferior limb of the primary U-loop of the gut-tube (Fig. 1432), increases in size until 

 it forms a conical pouch, joining the colon where the latter receives the small in- 

 testine. The growth of all parts of the caecum, however, is not uniform, sinc(i its 



^Anatom. Anzeiger, Bd. xvi., 1899. 



