DEVELOPMENT OF THE KErTU.M 27 



these projections is shown in figure 21 . In section 700 the inuscu- 

 laris mucosae has ahnost disappeared but traces of it can be found 

 in tlie form of a few scattered fibers lying (dose to the ei)ithelium, 

 particularly at the bases of th(^ folds. 



Between sections 700 and 750 are found the lower limits of the 

 secondary folds. These terminate as downward projections in 

 the form of tubules. Those belonging to the left ventral out- 

 folding are represented in figure 21. These tubular structures 

 are lined with a cuboidal epithelium of two to three layers of 

 cells and take on very much the appearance of glands. No evi- 

 dence that the epithelium is a glandular one, however, was obtain- 

 able anywiiere. Some of the tubules, about seven in number, 

 turn outward and come in contact with the internal sphincter 

 muscle. Two others pierce the internal sphincter and lie between 

 it and the outer longitudinal layer of nmscle, one of which is 

 shown in the figure. It is this type of tubule which Herrmann 

 descril^es under the term 'intramuscular sinus.' 



The lining epithelium of section 750 (fig. 2, E) is entirely strat- 

 ihed squamous, composed of seven to ten layers of cells. It 

 presents a few thickenings of the basal layer of cells which mark 

 the beginning of the hair follicles. It would seem from this that 

 this section was near the border line between the zona intermedia 

 and the zona cutanea. The superficial one to three layers of 

 squamous cells take the stain (orange G) more intensely and their 

 nuclei are smaller and more deeply staining than those of the 

 remaining layers, marking the beginning of a stratum corneum. 



In the section 800 (hg. 2, F) the zona cutanea proper is reached. 

 Here the epithelium is slightly thicker than above, but its chief 

 characteristic is the i:)resence of numerous hair follicles. The 

 irregularities of the ejHthelium are skin folds which extend radially 

 from the anal opening. Testut ('95) refers to these under the 

 term '' plis radies de I'anus" and Symington ('12) as the "anal 

 skin folds. " 



The longitudinal section of the rectum of an embryo of 1S7 mm. 

 represented in figm'e 3 shows well the topographical relations of 

 the \ari()us parts and structures of this region. The ampulla 

 recti is lined with the simple cohnnnar epithelium which for the 



