EPITHELIUM. 



Gl 



vessels and lymphatics are polished and smooth, and tho 

 interior of the heart is lined with membrane very similar to 

 the pericardium round it- 



39, Epithelium. All the free surfaces now alluded to 

 agree in one point, namely, that they are clothed with one 

 or more strata of nucleated corpuscles. Such investments 

 are termed epithelium, and the corpuscles which compose 

 them epithelial cells. 



Epithelia, in which the cells are arranged in a single layer, 

 are termed simple, while those in which there are several 

 layers, are distinguished as stratified; and stratified epithelia 

 are named according to the character of the superficial layer, 

 without regard to the numerous shapes of corpuscles in the 

 deep layers. 



In squamous or pavement epithelium the cells are flattened 

 like scales. The surface belonging to the third group above 

 described, including serous and sy no vial membranes, and the 

 interiors of vessels, are all clothed with simple squamous 

 epithelium of delicate microscopic character. The cuticle, 

 which will be more particularly described anon, and the 

 mucous membranes of the mouth, eyelids, and urinary 



Fig. S3. VARIETIES OF EPITHELIUM, a, separate squamous cells 

 from mouth ; 6, from serous membrane ; c, fluted cell from deep 

 part of epidermis ; d, columnar cells of intestine ; e, cubical cells 

 of kidney; /, ciliated columnar stratified epithelium of wind- 

 pipe ; g, ciliated spherical cells from choroid plexus of brain. 



