28 



EPITHELIAL TISSUES 



to thin flat scales on the surface is characteristic of all stratified 

 epithelium. 



The thin superficial scales resemble very closely in shape and 

 appearance the squamous epithelium previously described. The 



FIG. 27. EPIDERMIS OF THE SKIN OF THE FINGER TIP, SHOWING EXTREME KERATIZA- 

 TION OF THE EPITHELIUM. 



o, keratized epithelium ; 6. Malpighian or germinal layer ; c, connective tissue. 

 Hematein and eosin. x 50. 



deeper cells have a finely granular cytoplasm and distinct nuclei 

 except when obscured by the appearance of keratin within their 

 protoplasm. Many of these cells contain coarse granules of eleiclin 

 and Jceratohyalin substances chemically intermediate between the 

 unaltered and the keratized protoplasm. 



As stated, the formation of keratin within these cells is more 

 active in those membranes which are comparatively dry from ex- 

 posure to the air. Consequently, it is most active in the epidermis 

 of the skin. If stratified epithelium is at all times well moistened, 

 as, for example, in the mouth and esophagus, the formation of 

 keratin is slight, and the soft polyhedral cells compose the major 

 portion of the epithelial membrane which then has only a thin 

 superficial covering of flattened scaly cells. In the comparatively 

 dry epidermis, on the other hand, the flattened horny cells fre- 

 quently occupy more than half the thickness of the epithelial layer. 

 In the superficial squamous cells of moist membranes the nucleus 

 can always be readily demonstrated, even in the keratized cells of 

 the extreme surface. 



