274 



HISTOLOGY 



presents on its inner wall a number of longitudinal folds, known as rectal 

 columns (columns of Glisson or Morgagni). At their lower extremities 

 the columns unite with one another, thus forming small transverse plicae 



Rectal gland 



Linea ano-rectalis 



Zona columnaris 



Linea sinuosa analis 



Zona intermedia. 



Linea ano-cutanea 



Circular layer of 



smooth muscle. 



Longitudinal layer 

 of smooth muscle. 



Levator ani. 



Internal sphincter. 



Intramuscular gland. 



V, * 



External sphincter. 



Sheath of a hair. 



-Sebaceous gland. 



Zona cutanea. 



FIG. 270. LONGITUDINAL SECTION THROUGH THE PARS ANALIS RKCTI. 

 From a human embryo of 187 mm. (about four months) . (F. P. Johnson.) 



or anal valves. The grooves between the columns extend downward be- 

 hind the valves, forming a series of blind pockets, the sinus rectales. 



The mucous membrane of the first part of the rectum is similar to 

 that of the colon, but its glands are somewhat longer (0.7 mm.). Soli- 



