DEVELOPMENT OF THE RECTUM 37 



Plicae transversales recti 



The development of the pHcae transversales recti has been 

 described by Baur ('60). The few observations given below are 

 essentially in accordance with those of Baur. Apparently these 

 folds develop in a manner quite similar to the plicae circulares of 

 the small intestine and the plicae semilunares of the large intes- 

 tine, that is, by a gradual infolding of the mucous membrane. 



In an embryo of 70 mm. a careful macroscopic examination of 

 the rectal wall showed no evidence of transverse folds. At 99 

 mm., however, two small folds are perceptible in the lower portion 

 of the ampulla. At 140 mm. the transverse folds, which are 

 quite distinct, are arranged somewhat obliquely around the wall 

 of the ampulla recti. Three such folds are present, placed at 

 distances of 10 to 13 mm., 15 to 18 mm., and 20 to 22 mm. above 

 the anal opening. 



In an embryo of 187 mm. two small folds are present on the 

 right side at distances of 20 mm. and 25 mm. above the anus, 

 while a third larger fold is present on the left side, 30 mm. above 

 the anal opening. 



Out of four fetuses at birth the plicae transversales are present 

 in three. In the first case the lowest fold is on the left side 30 mm. 

 above the anal opening. Above this fold are two others both on 

 the right side at distances 40 mm. and 50 mm. above the anus. 

 As seen in figure 24, these folds extend around onto the left side 

 for a short distance. In the second fetus at birth, onlj^ two folds are 

 present, the lower being on the left side, while the upper is on the 

 right. These lie at distances of 35 mm. and 45 mm. above the 

 anus respectively. The third fetus likewise has two folds, but 

 the lower is on the right side and the higher on the left, at dis- 

 tances of 30 mm. and 40 mm. above the anus. In the fourth 

 fetus the plicae are entirely absent. The ampulla, however, is 

 very much distended with meconium, which probably in part 

 accounted for their absence. 



These obser\'ations are not entirely in accordance with those 

 of Otis ('87) who found that when two folds were present the 

 lowest was on the right side and the upper on the left, while when 

 three folds were present, the lowest was on the left side. 



