38 ELEMENTARY TISSUES. 



6. Tulules are formed of simple membrane, such as the 

 minute capillary lymph- and blood-vessels, the investing 

 sheaths of striated muscular and cerebro-spinal nerve- 

 fibres, and the basement membrane or proper wall of the 

 fine ducts of secreting glands. 



With these simple materials, the various parts of the 

 body are built up ; the more elementary tissues being, so 

 to speak, first compounded of them ; while these again 

 are variously mixed and interwoven to form more in- 

 tricate 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 

 materials wherewith to form arteries, veins and lympha- 

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

 other parts of the body. 



CHAPTEE V.* 



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 



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

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

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

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



