EPITHELIUM. 



41 



(a) Simple flat epithelium (epithelium of the lung alveoli, 

 the lining of the vessels, the pleural and peritoneal cavities, the 

 pericardium, the joint cavities, the tendon sheaths, etc.) ; 



(/?) Simple cubical epithelium (epithelium of the small 

 bronchi, some parts of the kidney tubules, the thyroid gland, 

 the ducts of many glands, etc.); ciliated cubical epithelium is 

 found in the oviduct, uterus, and fine bronchi) ; 



(y) Simple cylindrical epithelium (epithelium of many large 

 gland ducts, in the intestinal canal, etc.). 



(b) Stratified epithelium (Fig. 24) : 



(a) Stratified flat epithelium or pavement epithelium. The 

 superficial layers consist of flat cells (e. g., epithelium of the 

 cornea, the mouth cavity, the oasophagus, the skin, etc.) ; 



(/3) Stratified columnar epithelium. The most superficial 

 layer consists of columnar cells, the deepest layer of cubical or 

 polyhedral cells (e. g., in the ureter, the urinary bladder, etc.). 

 This is known also as transitional epithelium. The same sort 

 of epithelium, possessing also cilia, is found in the larynx, 

 trachea, large bronchi, vas deferens, epididymis, etc. 



Diagrams of epithelium: (a) nuclei at various levels; (ft) stratified pavement epithe- 

 lium ; (c) stratified cylindrical epithelium, ciliated at the right. 



An epithelium may consist of elements which are not all of 

 the same morphological significance. One often sees simple 

 cylindrical cells, ciliated cells, goblet cells, and cells with a striated 

 border in close association. 



As a transition stage between simple and stratified epithe- 

 lium, we have an epithelium in which the same cell reaches the 

 outer surface and also rests on the connective tissue at the base 

 of the epithelium (Fig. 24, a). The nuclei, which in typical 



