DEVELOPMENT OF THE LARGE INTESTINE 



195 



distinct folds are absent. The ridges are irregular in form and 

 of varjdng size, the largest being about 0.10 mm. in height. 

 The two types of cells are distinct now in this region of the large 

 intestine, some of which are like those which Patzelt has de- 

 scribed as drop-shaped. In many places large vacuoles similar 

 to those described above are found in the epithelium of the ridges. 

 The epithelial tube of the transverse colon is of the same size 

 as the ascending, and shows six well marked projections into 

 the lumen, two of which are folds. In the upper part of the 

 descending colon, two ridges and two folds are present. In the 

 iliac colon the folds drop out and only ridges are found. When 



Fig. V Cross section of the transverse colon of a human embrj^o of 50 mm. 

 X 60. 



followed downward, the descending colon shows more and more 

 ridges and when the sigmoid colon is reached there are as many 

 as ten or twelve. Still more caudally the rectum shows folds 

 which have taken the place of the ridges. In the lower part 

 of the rectum, just above the rectal ampulla, practically all the 

 ridges have been replaced by folds, varying from ten to four- 

 teen in number. The appearance obtained from cross sections, 

 therefore, is somewhat similar to that found in the stomach of 

 the same and slightly older embryos — the clefts in between the 

 ridges corresponding to the gastric pits. The clefts, however, 

 are broader and the cells of the epithelium lining them are more 



1 In this and all remaining text figures certain histological details have been 

 omitted. 



