2 FRANKLIN PARADISE JOHNSON 



gland cysts, which exist throughout a considerably long period 

 of embryonic life, but which have disappeared before birth. 

 These also have been described in the former paper. 



Regarding the material used and the method of study employed 

 very little need be said. Whole embryos, sectioned serially, have 

 been used for stages up to 44.3 mm. From this stage upward, 

 with the exception of an embryo of 65 mm. which was also 

 sectioned whole, the pars analis recti, including a portion of 

 the ampulla recti and the skin around the anus, was cut out of 

 the embryos and made into serial sections, some cross, and 

 some longitudinal. The serial sections of the whole embryos 

 obtained from the Harvard Embryological Collection are des- 

 ignated, H.E.C.; those from the collection of the University of 

 Missouri, H. 



Wax models have been made to illustrate the conditions at 

 various stages of development. Use was also made of gross dis- 

 sections, and particularly of mid-saggittal sections through the 

 whole pelvis. The models of the epithelial tube, except in case 

 of older stages, have been made at a magnification of 145 diam- 

 eters, and therefore allow eas}^ comparison with those made of 

 other portions of the digestive tube. 



A difficulty which presented itself at the outset of this work was 

 one concerning terminology. One finds in the literature varying 

 descriptions of the rectum; the same terms being used to denote 

 different portions. It was necessary, therefore, to review the 

 literature concerning the anatomy of the adult rectum and deter- 

 mine upon the most generally accepted terminology. A brief 

 review of the literature concerning the limits and subdivisions of 

 the rectum is first given. To it are added certain topographical 

 relations as described by various authors, for comparison with the 

 observations noted in the section on developmental topography 

 included in this paper. 



Although but few observations have been made regarding the 

 development of the plicae transversales recti, it was thought best 

 for the sake of completeness, as well as for comparison with the 

 observations made on the larger folds of the mucous membrane 

 found in the small and large intestines, to include a brief descrip- 



