DEVELOPMENT OF THE LARGE INTESTINE 205 



knoblike projections (0.11 to 0.14 mm. in length and 0.09 

 mm. in width), some of them appear to be double. As will be 

 subsequently described, this bifurcating of the glands is a very- 

 important factor in their multiplication. 



Conditions in the ascending colon, as regards villi and glands, 

 are similar to those in the transverse. In the rectum the epi- 

 thelial tube is again flattened laterally measuring 2.12 mm. by 

 0.69 mm. in cross section. The mucous membrane is thicker 

 (0.32 to 0.36 mm.) than that of the transverse colon (0.27 to 

 0.32 mm.). Its villi are from 0.22 to 0.27 mm. in height and its 

 glands about the same as those found in the transverse colon 

 (0.13 to 0.16 mm.). Goblet cells are again very numerous. 

 A few epithelial cysts were found in the extreme lower part of 

 the rectum, but these were almost insignificant in size as com- 

 pared to those of the former stages. 



Disappearance of villi 



In an embryo of 140 mm. the transverse colon has a diameter 

 of about 1.7 mm. and presents from thirty-six to forty longi- 

 tudinal rows of villi. It is apparent, therefore, that the ^'illi 

 are still increasing in numbers as the intestine is increasing in 

 size. Since no distinct longitudinal folds can be found in either 

 models or longitudinal sections, these additional villi must de- 

 velop from the beginning as separate growths in the spaces 

 between those villi already present. The form of the villi is 

 shown in figure 24. Some of the tallest measure only 0.25 mm. 

 in height. Disregarding the embryo of 120 mm., because of 

 the undoubted shrinkage of all its parts, and referring to the 

 110 mm. stage, it is seen that the villi are shorter in the older 

 embryo. Moreover, some of the villi are so short at 140 mm. 

 that the term villus is scarcely applicable to them, but whether 

 these are newly developed villi or dwindled-down old ones, I 

 am unable to determine. Although the intestinal glands vary 

 in length (0.13 to 0.18 mm.) they are on the whole slightly more 

 advanced than before and many show signs of bifurcating. From 

 the above observations it is evident that, as the glands are in- 



