SIMPLE EPITHELIA 



31 



uhlique aii<jjlt's to tlu'ir bases, such cells upj^ear as fusiform when the 

 central nuclear region is represented, or they ai)pear as a very 

 narrow hand with indistinct cellular outlines when sections miss the 

 nuclear ref2;ion. A simple squamous epithelium is found (Fig. S), 

 for example, forming Bowman's capsule of the uriniferous tubules 

 of the kidnev. 



Fig. 9. — Diagram of mesothelium. 



Fig. 10. — Diagram of endothelium. 



A membrane of squamous cells with wavy, irregular boundaries 

 forms the surface layer of the mesentery and the peritoneum of 

 mammals. (Fig. 9.) It is called mesothelium and ^'ery commonly 

 its cells have cilia from their free border. 



The ca\ities of the heart and all 

 blood and lymph vessels (Fig. 10) are 

 lined with a layer of elongated simple 

 squamous cells, similar to those of 

 the mesothelium. Their long axis is 

 usually directed along the line of flow 

 within the vessel. This simple squa- 

 mous type so located is called endo- 

 thelium. 



By subjecting fresh mesentery to a 

 weak bath of silver nitrate and bright 

 sunlight, a deposit of silver salt occurs 

 between adjoining cells and the cell 

 boundaries stand out clearly. In this 

 way it is possible to show the larger 

 mesothelial cells with wavy outlines 

 and the narrower and longer endothe- 

 lial cells forming the lining of small 

 vessels. 

 Simple Cuboidal Epithelium. — In this type the epithelial membrane 

 is composed of cells whose three dimensions are approximately 

 equal and ap])ear in sections as rough squares. Cuboidal epithelium 

 is found in portions of the excretory ducts of many glands and in 

 certain areas of the uriniferous tubules of the kidney. (Fig. 11.) 



Fig. 11. — Photograph of simple 

 ruboidal epithelium of a collecting 

 tubule of the rat kidney. Sur- 

 rounding it are a number of capil- 

 laries with walls composed of 

 simple squamous cells. 



