20 



HAND-BOOK OF PHYSIOLOGY. 



CLASSIFICATION OF EPITHELIAL CELLS. 



Epithelial cells may be conveniently classified as: 



1. Sguamous, scaly, pavement, or tessellated. 



2. Spheroidal, glandular, or polyhedral 



3. Columnar, cylindrical) conical, or goblet-shaped. 



4. Ciliated. 



5. Transitional. 



Although, for convenience, epithelial cells are thus classified, yet the 

 first three forms of cells are sometimes met with at different depths in 



FIG. 11. Vertical section of Rabbit's cornea, a. Anterior epithelium, showing the different 

 shapes of the cells at various depths from the free surface, b. Portion of the substance of cornea. 

 (Klein.) 



the same membrane. As an example of such a laminated epithelium 

 showing these different cell-forms at various depths, we may select the 

 anterior epithelium of the cornea (Fig. 11). 



1. Sguamous Epithelium (Fig. 12). Arranged. (A) in several super- 

 posed layers (stratified or laminated), this form of epithelium covers (a) 

 the skin, where it is called the Epidermis, and lines (b) the mouth, 



pharynx, and oesophagus, (c) the conjunc- 

 tiva, (d) the vagina, and entrance of the 

 urethra in both sexes; while, as (B) a single 

 layer, the same kind of epithelium forms 

 (a) the pigmentary layer of the retina, 

 and lines (b) the interior of the serous and 

 synoviul sacs, and (c) of the heart, blood 

 and lymph- vessels (Endothelium). It con- 

 sists of cells, which are flattened and scaly, 

 with an irregular outline: and, when laminated, may form a dense horny 

 investment, as on parts of the palms of the hands and soles of the feet. 

 The nucleus is often not apparent. The really cellular nature of even 

 the dry and shriveled scales cast off from the surface of the epidermis, 

 can be proved by the application of caustic potash, which causes them 

 rapidly to swell and assume their original form. 



FIG. 12. Squamous epithelium scales 

 from the inside of the mouth. X 260. 

 (Henle.) 



