DEVELOPMENT OF THE RECTUM 31 



down onto tlic aiitcrioi' hordci' of the fhittciKHl zona intermedia. 

 The post(M-ior i)i-iinai'y fold passt^s into the posterioi- border of the 

 same, while the rij>;ht fold terminates on the side of the zona inter- 

 media. The secondary folds are more numerous than in the 

 abo"S'e-des('ribed stages. Of these there are about twelve on the 

 left primary fold, twenty-two on the right, and about twenty-six 

 on the left, about sixty in all. 



Extending outward from this region are to be seen the intramus- 

 cular glands. These are more highly developed in the lower por- 

 tions than abo\e. Some few which did not lend themselves 

 easily to modeling are not shown in the figiu'es. The intramuscu- 

 lar glands extend out from the stratified columnar epithelium of 

 the zona columnaris. Some of them are solid cords of cells 

 throughout, others ha\'e distinct lumens, while still others have 

 lumens only in certain portions. Those with lumens are lined by 

 an epithelium of two to three layers of cells, the uppermost of 

 which are in man}- places columnar and suggestive of secretory 

 cells. 



The zona intermedia, owing to distention caused by the pres- 

 ence of meconium in this region, is not so flattened as in the pre- 

 ceding stages. The larger folds of the zona columnaris are pro- 

 longed down onto this region and gi\'e it an irregular appearance. 

 Several of these folds are directly continuous with the skin folds 

 of the zona cutanea. The zona intermedia is lined with a strati- 

 fied squamous epithelium of from six to fifteen layers of cells, the 

 uppermost of which show distinct cornification. The epithelium 

 is thickest between the infoldings (0.07 mm.) and thinnest on 

 their tops (0..32 mm.). AMth the exception of one sebaceous 

 gland (without a hair shaft) which is present high uj) on the right 

 side of the zona intermedia, no other glands or follicles are pres- 

 ent in this region. A considerable distance further down hair 

 follicles and sebaceous glands appear and mark the beginning of 

 the zona cutanea. The zona cutanea is lined with a stratified 

 squamous epithelium of 0.03 to 0.30 mm. thick and is composed of 

 five to ten layers of cells. It is distinctly cornified and shows 

 nmnei'ous ])apillae, hair follicles, and sebaceous glantls. 



