224 FRANKLIN PARADISE JOHNSON 



CONCLUSrOXS 



1. The large intestine, like the oesophagus, stomach, and 

 small intestine, is at first a simple tube of epithelium, and is the 

 last portion of the digestive tube to show distinctive changes 

 in the form of its mucosa. The first change which occurs is the 

 formation of longitudinal folds and ridges. 



2. The ridges and folds first appear in the rectum and then 

 extend upward (orally). A second point of growth is found in 

 the ascending colon at the colic valve. The direction of growth 

 here is in the opposite direction (aborally). The transverse 

 colon is the last portion of the large intestine to develop ridges 

 and folds. 



3. A few vacuoles similar to those found in the oesophagus, 

 stomach, and small intestine, are found in the epithelial wall of 

 the large intestine in its early stages. 



4. The longitudinal folds are replaced by villi in a manner 

 which suggests a segmenting of folds. However, it is not im- 

 probable that the villi of the large intestine arise after the manner 

 of those of the small intestine, as separate growths along the 

 tops of the folds. 



5. Additional villi arise as separate growths between those 

 villi already formed, not being preceded by folds. 



6. The first glands appear as knob-like protuberances of the 

 epithelium into the underlying mesenchyma. Additional glands 

 develop by a splitting, from below upwards, of those already 

 formed. 



7. Villi reach their maximum height in embryos between 110 

 mm. and 140 mm. in length. From this time on they gradually 

 become smaller in size. Remnants of them persist as folds 

 which form an irregular network in between the gland openings. 

 They are entirely gone at birth. 



8. In the vermiform process villi and glands develop, and the 

 villi disappear at the same time and in the same manner as 

 those of the ascending colon. 



9. Enlarged and cystic glands are found in the vermiform 

 process and caecum. Many of them become detached from the 



