STRATIFIED SQVAMOUS EPITHELIUM. 



43 



the epithelium of the kidneys, ureters, and sexual organs, 

 which is mostly of mesoblastic origin. 



Its function is, over large areas, protective ; in the glands 

 it is secretory ; in some tracts, as the intestine, it is not only 

 protective, but has absorbent functions; while ciliated and 

 other epithelium serve special purposes. 



Varieties of epithelium: Epithelium-cells may be divided 

 into the following classes : squamous, columnar, ciliated, gob- 

 let, glandular, and specialized epithelium. Some of these, 

 again, are divisible into simple epithelium, in which the cells 

 form a single layer; and stratified, in which they are arranged 

 in several layers. 



Simple squamous epithelium : Squamous epithelium-cells are 

 large, thin, flat, disc-shaped cells, each with a large discoid 

 nucleus. In simple squamous epithelium the cells form but 

 a single layer, and meet edge to edge. It is not extensively 

 distributed, occurring in the alveoli of the lungs, the capsule 

 of the Malpighian bodies of the kidney, and a few other situa- 

 tions. Endothelium is very similar to it. 



FIG. 11. 



Stratified squamous epithelium, oesophagus of rabbit (Dunham), a, deeper layers 

 of rounded germinal cells ; b, more superficial layers of flattened cells ; c, sur- 

 face layer of horny cells ; d, underlying fibrous tissue ; e, papillary projection 

 from the fibrous layer. 



In stratified squamous epithelium the cells form several 

 layers (Fig. 11). Those on the surface are flattened and 

 squamous, overlapping one another at the edges. The cells 

 of the lower layers are cuboidal or spheroidal ; they become 



