38 FRANKLIN PARADISE JOHNSON 



With regard to the direction of the folds it may be said that in 

 practically no case did the folds run directly transverse to the 

 long axis of the rectum. Usually they were placed somewhat 

 obliquely. However, in no instance did they have a distinct 

 spiral arrangement around the wall of the rectum, after the man- 

 ner described by Vance. 



The relation of the developing rectum to the vertebral column 



Along with the development and descent of the various struc- 

 tures and organs of the pelvis, there take place corresponding 

 changes in the position of the rectum. These changes are par- 

 ticularly noticable in case of the pars analis recti which, in its 

 early stages, lies at a higher level and is relatively greater in its 

 extent than in the later stages. WTiereas in the adult the first 

 portion of the rectum begins at the level of the third sacral verte- 

 bra (by definition) and lies along the concavity of the remainder 

 of the sacrum and coccyx, in very early stages this portion of the 

 rectum is found above the third sacral vertebra. Likewise the 

 pars analis recti which in the adult is an inch or more in front of 

 and below the tip of the coccyx, early is found occupying a posi- 

 tion extending from the third sacral vertebra to the tip of the 

 coccjrx. The determination of such relations has only been made 

 possible through the existence of the bulbus analis, which as has 

 been shown, is present as a swelling throughout stages up to birth, 

 and which forms in a large part the zona columnaris. 



In an embryo of 16 mm. (H. 133) the spindle-shaped bulbus 

 analis lies along the concavity of the sacrum. Its upper limit 

 lies on a level with the third or fourth sacral vertebra. The anus 

 is found in the neighborhood of the second or third coccygeal 

 vertebra. Such levels, however, can only be approximately 

 determined. This is because the epithelial tube of the rectum 

 does not lie directly against the bodies of the vertebra, and 

 because of the great curvature of the body in this region. The 

 long axis of the embryo in this region, therefore, is a much curved 

 line. 



In figure 6, A are seen the relations which exist in an embryo 

 of 28.8 mm. (H.E.C. 1598). The upper portion of the bulbus 



