EPITHELIUM 



49 



columnar and closely crowded. They multiply by mitosis and give rise 

 to cells which are pushed toward the free surface. After leaving the basal 

 layer they enlarge and become polygonal in outline. Toward the free 

 surface they become gradually flattened, and may be more or less cornified 

 or transformed into horny material. These scale-like ^ells are called 



Cut. 



Ter. b. 



FIG. 35. SIMPLE COLUMNAR EPITHELIUM FIG. 36. -DETACHED SQUA- FIG. 3 7- STRATIFIED EPITHE- 



FROM A HUMAN INTESTINAL VILLUS. MOU s CELLS FROM THE HUM FROM THE CESOPHAGUS 



A, Surface view; B, vertical section. The MOUTH. OF A CHILD. 



prominent cell outlines in A are due to 



terminal bars, shown in section in B. 



Cut., cuticular border. 



squamous cells and they readily become detached (Fig. 36). Stratified 

 epithelium is found in the vagina, oesophagus, pharynx and oral cavity; 

 and in its most complex form, with many layers, some of which are pecu- 

 liarly modified, it constitutes the epidermis. 



'Columnar cells" 



.Fusiform cells- 



> -Basal cells 



-Conn, tisues. 



FIG. 38. 



FIG. 39. 



FlGS. 38 AND 39. PSEUDO-STRATIFIED CILIATED EPITHELIUM FROM THE HUMAN RESPIRATORY TRACT. 



Fig. 39 is a diagram of the condition shown in Fig. 38. X72O. 



In certain organs and especially in embryos, simpler forms of stratified 

 epithelium occur, which are described as four-layered, or two-layered as 

 the case may be. The superficial cells may be flat, cuboidal, or columnar. 

 A characteristic epithelium with dome-shaped outer cells and tall basal 

 cells, found in the bladder and ureter, is known as "transitional epithe- 



4 



