DEVELOPMENT OF THE LARGE INTESTINE 201 



bases. The tops of the vilH are in many places so closely approxi- 

 mated that it is quite impossible from cross sections of this stage 

 alone to determine whether an actual fusion has or has not taken 

 place. Because of this condition, which I beheve to have been 

 brought about by a strong contraction of the muscularis, an 

 attempt to model these villi accurately proved fruitless. From 

 the conditions found in the large intestine, of other embryos 

 of about the same age, however, it would not seem probable 

 that such a thing as an actual fusion had taken place. The 

 epithelium on the tops of the projections is distinctly one-layered 

 and 0.025 to 0.028 mm. thick, while between them it appears 





'4 



Fig. 4 Cross section of the transverse colon of a human embryo of 88 mm. 

 X60. 



two-layered, and is almost twice as thick, 0.042 to 0.052. Only 

 the portions of the epithelium in between villi are provided with 

 distinct basement membranes. 



In the descending colon practically the same conditions are 

 repeated, with the exception that a few more villi are present. 



In the transverse colon at 75 mm., even though considerable 

 shrinkage is present, the villi are seen distinctly separated from 

 one another. Other portions of the large intestine from the 

 two last-mentioned embryos were not obtained. 



In the transverse colon of an embr3^o of 88 mm. (fig. 4), are 

 found numerous villi, which are arranged so that they form 

 longitudinal rows. The epithelium on the tops and sides of the 

 villi is similar to that of the preceding stages, being simple colum- 

 nar in form and containing goblet cells. Between the villi the 

 cells are tall cylindrical and conical in shape, contain oval nuclei 



