DEVELOPMENT OF THE LARGE INTESTINE 



203 



mm. Although shrunken from the underlying mesenchyma, 

 the epithelial tube has increased to 1.03 mm. in diameter. The 

 sigmoid colon has a diameter of 0.95 mm. and an epithelium 

 which is similar in variety and of equal thickness to that just 

 described. 



From this point on, measurements taken of the glands and 

 villi can only be considered approximately accurate. This is 

 due to the fact that there is no sharp line of demarcation between 

 gland and villus, consequently one is unable to determine just 

 where the gland begins and where the villus leaves off. A simi- 

 lar difficulty was met with in the case of the small intestine. 

 It is, however, possible, with the aid of models for comparison, 







Fig. 5 Cross section of the transverse colon of a human embryo of 110 mm. 

 X 60. 



to judge the line of division approximately. In the following 

 account of the growth of glands and villi, the figures given are 

 the average of a number of measurements made from cross or 

 longitudinal sections, or in some cases, from both. A more 

 accurate method, which was employed whenever possible, was 

 the direct measurement of these structures from the models 

 themselves. In the transverse colon of the embryo under de- 

 scription (99 mm.), the glands may be regarded as about 0.07 

 mm. long and 0.056 mm. broad, while the villi as 0.27 mm. 

 tall and 0.10 mm. broad. In the sigmoid colon the glands aver- 

 age 0.10 mm. and the villi 0.31 mm. in length. 



