214 FRANKLIN PARADISE JOHNSON 



side. For the most part the mouths of the glands open singl}^ 

 to the surface, but in one region of the model, three can be seen 

 opening together in a slightly depressed region of the surface 

 epithelium. The glands are still of the simple and ))ifurcated 

 tj'pes, the bifurcated ones representing different stages in the 

 process of splitting. The epithelium, which is similar to that 

 in the adult, is 0.017 mm. in thickness at the surface, while in 

 the glands it measures 0.28 mm. Goblet cells are still numer- 

 ous. Measurements made from cross sections of the transverse 

 colon at birth are as follows: 



Diameter of epithelial tube 5.5 mm. 



Perimeter 39.0 mm. 



Thickness of mucosa 0.25 mm. 



Thickness of outer coats 0.27-0.72 mm. 



Number of glands 384 . 



Number of glands per millimeter 9.8 



Summary 



To the foregoing observations the following summary may be 

 added. As has been pointed out before, the cylindrical tube of 

 epithelium of the early stages develops longitudinal thickenings 

 or ridges. In an embryo of 58 mm. these are becoming par- 

 tially transformed into low longitudinal folds. In embryos of 

 65 mm. these folds apparently segment, and in embryos of 88 

 to 99 mm. true villi are present. We have, therefore, longi- 

 tudinal folds apparently subdivided to form villi. This view 

 concerning the formation of the villi in the small intestine has 

 been presented by Berry ('00) and confirmed by Forssner ('07). 

 In opposition to this, the view that the villi arise as separate 

 growths of the epitlu^lium, not preceded by folds, has been 

 maintained by Koelliker ('61 and '79), Earth ('68), and Brand 

 ('77). Voigt ('99) believed that the surface epithelium was cut 

 up into a number of elevations by a net work of fissures and 

 furrows, and that these elevations grew into villi. In a study 

 of the development of the whole of the human small intestine 

 the present author ('10) wrote: 



