138 PRACTICAL MICROSCOPY. 



ordinary elements.) (g) The absence of any special basement 

 membrane. 



8. The abrupt transition from columnar to flattened cells in 

 the epithelium of the external os. (a) The shortening of the 

 columnar cells as the point of change is approached. (Sections 

 must be examined until one is found showing this point well. The 

 illustration (Fig. 93) is not exaggerated, and a properly cut and 

 selected specimen must exhibit clearly the last columnar and the 

 adjoining flattened cell. I know of no location in the human body 



FIG. 93. EXTERNAL Os OF FIG. 9,2. MORE HIGHLY MAGNIFIED. X 400, 



A. Muscular tissue of the os uteri, with numerous blood-vesseis. 



B. Capillary plexuses of subepithelial tissue mucosa. 



C. Ciliated columnar cells covering the os. 



D. Vacuolated cells. 



E. Shortening of the columnar cells preparatory to 



F. Change from typical uterine epithelia ciliated columnar cells to flattened, stratified 

 cells. 



G. Papillary structure of the mucosa of the external os, after the change of epithelium. 



where the change in form of cell covering approaches this in abrupt- 

 ness.) 



9. The vaginal epithelium (Figs. 93 and 94). (a) That it is of 

 the stratified variety, (b) The deepest line of cells following the 



