EPITHELIUM. 271 



irregularly oval, these cells vary somewhat, those on the surface 

 being more flattened than those of the deeper layers, which are 

 more spherical in form. They contain protoplasm, a nucleus, and 

 a number of granules. The superficial cells are eventually cast 

 off, the deeper ones taking their place, and the latter become more 

 and more flattened as they approach the surface. Consisting 

 thus of layers or strata of cells, the name stratified epithelium 

 has been applied to this tissue ; it is found in the alimentary 

 mucous membrane, from the mouth to the first half of the 

 stomach, in the bladder, the rectum, the entrances to the nose, 

 the eye, urethra, and vagina, and in a dried and desquamating 

 form it constitutes the epidermis or scarf skin ; it is non-vascular, 

 and for the most part non-sensitive. 



Endotheliiiin. — This resembles epithelium in structure, difter- 

 ing in its situation, as above described, and in the fact that it is 

 arranged as a single layer of flattened cells. 



Columnar or cylindrical epithelium. — In this variety the cells 

 are cylindrical in form, and arranged side by side, with their 

 long axes perpendicular to the subjacent surface. Their contents 

 resemble those of the squamous kind, but the nucleus is more 

 distinct. This form of epithelium is found on the mucous 

 membrane of the intestines and pyloric half of the stomach, and 

 it is continued into the ducts of the glands which open on the 

 surface of the membrane. The cells covering the villi of the 

 intestine have expanded free extremities, which may appear 

 slightly striped. 



Spheroidal or Polyhedral epithelium is found in the follicles 

 and ducts of glands, hence the name glandular epithelium. The 

 cells of this variety are spheroidal, or it may be irregularly poly- 

 hedral in shape. A variety known as transitional occurs in the 

 mucous membrane of the urinary 

 bladder, the cells being transi- 

 tional in form between those of 

 columnar and scaly kinds, and 

 arranged in a small number of 

 layers. F'^- ^o- 



/^•7» ,7 -J.! T • J. r Ciliated epithelium, highly masjnified. 



Clhated epithelium consists of „_ Nucleated cells ; ft, Cilia. 



columnar cells, provided at their 



free extremities with delicate hair-like processes or cilia, which 

 wave to and fro in a marked manner. The motion is apparently 

 independent of the direct influence of the nervous system, since it 



