|Crown-Rump Length (mm)||Diameter of epithelial tube||Perimeter, measured at bases of glands||Thickness of mucosa||Thickness of outer layers||Number of glands touching muscularis mucosae||Number of glands per running millimeter|
|200||3.5 mm.||11.1 mm.||0.40 mm.||0.27 mm.||75.0||6.7|
Fetus 200 mm
In the transverse colon of an embryo of 200 mm. practically the same conditions as those described for the sigmoid colon of the 190 mm. stage are encountered. The mucous membrane, although not thrown up into folds, does not appear stretched out. The villi are of various sizes, the tallest being from 0.14 to 0.18 mm. high. The intestinal glands measure from 0.18 to 0.22 mm. in length. Other measurements taken are as follows:
Diameter of epithelial tube 3.5 mm.
Perimeter, measured at bases of glands 11.1 mm.
Thickness of mucosa 0.40 mm.
Thickness of outer layers .027 mm.
Number of glands touching muscularis mucosae 75.0
Number of glands per running millimeter 6.7
Fetus 240 mm
In an embryo of 240 mm. the transverse colon shows some distention, but not so much as was seen in this portion of the large intestine at 190 mm. This is made evident by comparing the thicknesses of the mucosa and the outer coats. As seen in a model (not ﬁgured), made at double the magniﬁcation of the former model, the mucous membrane presents on its lumen surface a number of large irregular anastomesing folds. Between the folds are clefts, which in some places appear to be the glands themselves; in other places they are merely crypts into which the glands open. The glands are, for the greater part, of the simple tubular type, but some show bifurcations into two or three portions. The epithelium, which varies in thickness from 0.020 to 0.034 mm., is made up of the typical simple columnar cells found in the adult intestine, and contains large numbers of goblet cells. The following list of measurements is given for comparison with the other stages:
Total diameter of epithelial tube 4.6 mm.
Perimeter, measured at the bases of the glands 14.8 mm.
Thickness of mucosa 0.36 mm.
Thickness of outer coats 0.22 mm.
Number of glands touching muscularis mucosae 1140
Number of glands per running millimeter 7.7
Fetus 320 mm
In an embryo of 320 mm. a piece of transverse colon which was greatly distended with meconium was examined. The large folds of the mucosa have all disappeared and the intestinal wall as a whole is considerably thinned out. Owing to poor preservation, however, it was not possible to determine the presence of villi and folds. Measurements made are as follows:
Total diameter of epithelial tube 5.5 X 14.5 mm.
Perimeter, measured as before 34.7 mm.
Thickness of mucosa 0.16 mm.
Thickness of outer coats 0.20 mm.
NuIr1l)er of glands 269.0
Number of glands per millimeter 47.7
Fetus 7 months
In a fetus of about seven months (premature birth) the ascending colon seems to be almost entirely devoid of villi and the before-described folds. Although not modelled, it is plain to see that the surface epithelium is for the most part, though not entirely, level. At more or less regular intervals, it dips down into the cylindrical intestinal glands. Measurements:
Total diameter of epithelial 3.7 mm.
Perimeter 8.5 mm.
Thickness of mucosa 0.27 mm.
Thickness of outer coats 0.54 mm.
Number of glands 162.0
Number of glands per millimeter 8.’?
Sections of the sigmoid colon show a similar condition as regards glands. They are of an equal length and similarly distributed.
In a fully developed fetus at birth (ﬁg. 8), a condition is reached in which the villi have entirely disappeared. A model of a portion of the epithelium of the transverse colon is shown in figure 25. As seen from the model, only glands are present, the openings of which appear irregular when viewed from the lumen side. For the most part the mouths of the glands open singly 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 bifurcated types, the bifurcated cries 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 numerous. 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.
’l‘hic-liness of mucosa 0.25 mm.
Thickness of outer coats 0.27-0.72 mm.
Number of glands 3840
Number of glands per millimeter 9.8