2() FRANKLIN PARADISE JOHNSON 



fi])ers antl few iier\'e cells enil^eclded in the connective tissue. 

 Separated from the outer longitudinal muscle coat h^y a thin band 

 of connective tissue is seen a third heavy layer of muscle fibers, 

 . the levator ani. Already striations can be made out in these 

 fibers. At the level of section ()()() the fibers of the levator ani are 

 arranged circularly, but the ring is discontinuous both ventrally 

 and dorsally. 



In section 650 the villi and the intestinal glands have for the 

 greater part disappeared, although several can be seen in the 

 immediate region of those labelled in the figure. The epithelium 

 lining these is the same as before. In the remainder of the tube 

 the epithelium is stratified, composed of three to four layers of 

 low columnar cells. The protoplasm of these cells is finely gran- 

 ular and stains more intensely than that of the cells in the glands. 

 The transition between this epithelium and that of the ampulla 

 recti is gradual and forms the ano-rectal line. Since section 650 

 passes through the bulbus analis. it becomes evident that the 

 histologically-described ano-rectal line lies within this swelling 

 and does not correspond in position to the constriction between 

 the l)ulbus analis and the ampulla recti. Few goblet cells appear 

 in the stratified epithelium below the ano-rectal line but these 

 become fewer and fewer and finally disappear when followed 

 downward. The remaining outward projections of the epithe- 

 lium in the figure, namely those which are not glands, are secon- 

 dary outfoldings. 



In section 700 (fig. 2, D) glands, villi and intestinal epithelium 

 with its goblet cells, have entirely disappeared. However the 

 stratified columnar epithelium does not pre\'ail throughout for on 

 the summits of the ventral and left primary infoldings, a stratified 

 squamous epithelium has made its appearance. This gradually 

 becomes thicker and more extensive as the anal canal is followed 

 caudally. The transition between this and the stratified colum- 

 nar epithelium (linea sinuosa analis) is, as pointed out by Herr- 

 mann, gradual. 



The gland-like pi'otuberances seen in the \entral fold of section 

 700 are merely the downward projections of the ends of folds, 

 similar to those seen all around the tube. A model of some of 



