EPITHELIUM. 



35 



several superposed layers this form of epithelium covers the 

 skin, where it is called the Epidermis, and is spread over the 

 mouth, pharynx, and oesophagus, the conjunctiva covering the 

 eye, the vagina, and entrance of the urethra in both sexes; 

 while, as a single layer the same kind of epithelium lines the 

 interior of most of the serous and synovial sacs, and of the 

 heart, bloodvessels, and lymphvessels. 



2. Another variety of epithelium named spheroidal, from 

 the usually more or less rounded outline of the cells composing 

 it (d, Fig. 3), is found chiefly lining the interior of the ducts 

 of the compound glands, and more or less completely filling 

 the small sacculations or acini, in which they terminate. It 

 commonly indeed occupies the true secreting parts of all 

 glands, and hence is sometimes called glandular epithelium 



The gastric glands of the human stomach (magnified), a, deep part of a pyloric 

 gastric gland (from Kolliker); the cylindrical epithelium is traceable to the cseeal 

 extremities, b and c, cardiac gastric glands (from Allen Thomson); ft, vertical sec- 

 tion of a small portion of the mucous membrane with the glands magnified 30 diame- 

 ters; c, deeper portion of one of the glands, magnified Go diameters, showing a slight 

 division of the tubes, and a sacculated appearance produced by the large glandular 

 cells within them ; d, cellular elements of the cardiac glands magnified 230 diameters. 



(b, c, and d, Fig. 3). Often, from mutual pressure, the cells 

 acquire a polygonal outline. From the fact, however, of the 

 term spheroidal epithelium being a generic one for almost all 

 gland-cells, the shapes and sizes of the cells composing this 

 variety of epithelium are, as might be expected, very diverse 

 in different parts of the body. 



3. The third variety is the cylindrical or columnar epithelium 

 (Figs. 4 and 5), which extends from the cardiac orifice of the 



