Mucous Membrane in the Human Embryo. 5di7 
3. At first the basal surface of the epithelium shows no irreg- 
ularities due to the gastric pits. Then appear slight swellings 
into the mesenchyma. Still later depressions or furrows, alter- 
nating with the gastric pits, extend inward into the epithelium 
from the mesenchymal surface. This brings about a readjust- 
ment of the cells, and causes the heretofore 2 to 3 layered epithe- 
lium to become single layered. 
4. The groove-like pits anastomose with one another to form 
a network. This network marks out irregular areas of the surface 
epithelium, which have been described as villi. 
5. Growth of the mucous membrane is accompanied by an 
increase in the number of pits and by an increase in their size. 
The additional pits develop in between those already formed. 
6. Glands, first seen at 120 mm., bud out from the bottoms 
of the pits. These rapidly increase in number and give off 
branches. Parietal cells are first distinct at 120 mm. 
7. Large longitudinal folds of the mucous membrane occur in 
the stomach, but are variable in position, number, and size. 
Their occurrence is probably due to the contraction of the mus- 
cularis. 
Small intestine 
1. Vacuoles occur in the epithelium of the duodenum of em- 
bryos ranging from 10 mm. to 24mm. Inembryos of 16mm. and 
22.8 mm. the vacuoles were found to lead to a complete occlusion 
of the duodenal lumen. In an embryo of 19 mm. some of the vac- 
uoles were found to be arranged so as to form small ‘duodenal 
pockets.” These resemble the intestinal pockets of the jejunum 
and the ileum. It is probable that these duodenal pockets are 
transition forms between the vacuoles of the upper part of the di- 
gestive tube and the intestinal pockets of the lower part. In the 
duodenum at 134 mm. several small epithelial cysts were found. 
It is possible that these are vacuoles or duodenal pockets which 
have persisted. 
2. In the jejunum and ileum intestinal pockets, similar to 
those described by Keibel, Lewis and Thyng, and Elze, were found. 
