EPITHELIUM. 29 



body are built up ; t;he more elementary tissues being, so 

 to speak, first compounded of them; while these again 

 are variously mixed and interwoven to form more intricate 

 combinations. Thus are constructed epithelium and its 

 modifications, connective tissue, fat, cartilage, bone, the 

 fibres of muscle and nerve, etc. ; and these again, with the 

 more simple structures before mentioned, are used as mate- 

 rials wherewith to form arteries, veins, and lymphatics, 

 secreting and vascular glands, lungs, heart, liver, and other 

 parts of the body. 



CHAPTER IV.* 



STRUCTURE OF THE ELEMENTARY TISSUES. 



Epithelium. 



ONE of the simplest of the elementary structures of which 

 the human body is made up, is that which has received the 

 name of Epithelium. Composed of nucleated cells which are 

 arranged most commonly in the form of a continuous 

 membrane, it lines the free surfaces both of the inside and 

 outside of the body, and its varieties, with one exception, 

 have been named after the shapes which the individual 

 cells in different parts assume. Classified thus, Epithelium 

 presents itself under four principal forms, the characters 

 of each of which are distinct enough in well-marked ex- 

 amples; but when, as frequently happens, a continuous 



* The following Chapter, containing an outline- description of the 

 elementary tissues, has been inserted for the convenience of students. 

 For a much fuller and better account, the reader may be referred to 

 Dr. Sharpey's admirable descriptions in Quain's Anatomy. 



