THE DEVELOPMENT OF THE RECTUM IN THE 

 HUMAN EMBRYO 



FRANKLIN PARADISE JOHNSON 



The Anatomical Laboratory of the University of Missouri 



TWENTY-FIVE FIGURES 



INTRODUCTION 



This is the third of a series of papers concerning the develop- 

 ment of the mucous membrane of the digestive tract. The 

 first two (Johnson '10 and '13) deal with the oesophagus, stomach, 

 and small and large intestines. In this paper an account of the 

 development of the rectum is given, particular attention being 

 paid to the formation of the pars analis recti. 



The upper portion of the rectum, that is, that part which goes 

 into the formation of the ampulla recti, develops in a similar 

 manner to the colon. In this region, ridges, folds, villi, and 

 glands make their appearance in the order named, and, simul- 

 taneously with the further development of glands, the villi dis- 

 appear. As these changes have already been described by stages, 

 another account need not be given here. Attention, however, 

 might again be called to the fact that the rectum is more preco- 

 cious in its development than the other parts of the large intes- 

 tine; thus we find in the rectum conditions which are always in 

 advance of those higher up. It is to be noted also that the ridges 

 and folds of the mucous membrane which precede the formation 

 of glands and villi, at the level where these pass over into the anal 

 region, are not longitudinal in direction, as found in the remaining 

 portions of the large gut, but are transverse. In still another 

 respect the mucous membrane of the ampulla recti of the embryo 

 differs from that of the colon. One finds numerous epithelial 



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THE AMERICAX JODRNAL OP ANATOMT, VOL. 16, NO. 1 

 MARCH, 1914 



