DEVELOPMENT OF THE RECTUM 45 



of acini, is to be found a small amount of lymphoid tissue. The 

 epithelium lining the glands is made up of several layers of polyg- 

 onal cells in the main ducts, but in the ampullae and branches it 

 is composed of one to two layers of cuboidal cells. It is claimed 

 that evidences of secretory cells are wanting in the adult, but 

 in the fetus and at birth they are present. 



Tn his summary, Braun tabulates the epithelia of the zona col- 

 umnaris as follows : 



(a) Einfaches Cylinderepithel findet sich in dem proximalen Teil der 

 Columnen ; in dem proximalen Teil der Sinus ; in alien Lieberkiihnschen 

 Driisen; am unteren, blinden Ende der rohrenformigen Anhange der 

 Ausbuchtungen der Sinus. 



(b) Geschichtetes Cylinderepithel findet sich in dem distalen Ab- 

 schnitte der Sinus; auf den die Sinus begrenzenden Flachen der Colum- 

 nen; in den sekundaren Ausbuchtungen der Sinus; in den Ausfiih- 

 rungsgangen der rohrenformigen Anhange der Ausbuchtungen. 



(c) Geschichtetes Plattenepithel (polyedrisches Epithel) findet sich 

 auf der Hohe der Columnen in ihrem distalen Abschnitt. 



The results of my own work regarding the epithelium of the 

 zona columnaris are in accordance with the above tabulation, but 

 I must also add that: 



(d) Stratified cuboidal epithelium is found in the larger ducts of the 

 intramuscular glands. 



(e) Simple cuboidal epithelium is found in the branches of the intra- 

 muscular glands. ' 



The zone intermedia is lined by a stratified squamous epithe- 

 lium. This is composed of several layers of polygonal cells form- 

 ing a thicker layer than the epidermis of the skin. Dermal 

 papillae are present, but hairs and sweat glands are absent. In 

 the lower part of this zone may be found a few isolated sebaceous 

 glands without hairs, and a slight amount of cornification of the 

 epithelium. The transition between the epithelium of this zone 

 and that of the zona columnaris is rather abrupt. It lies at the 

 level of the anal valves, but in between the vah^es it extends up- 

 ward on the summits of the rectal columns. It thus forms a zig- 

 zag line, which is known as the linea sinuosa analis (ano-cutaneous 

 line of Herrmann). At its lower limit the zona intermedia grad- 

 ually goes over into the skin. The transition here forms the true 



