CHAPTER II. 

 THE ELEMENTARY TISSUES. 



THE tissues which make up the various organs and parts 

 of the body may be divided into the following groups: (i) Epi- 

 thelial tissue, (2) connective tissue, (3) muscular tissue and (4) 

 nervous tissue. 



The Epithelial Tissues. 



The epithelial tissues include those which form the covering 

 for the body, the lining of the digestive canal, the respiratory 

 tract and the genito-urinary tract. They also constitute the 

 derivatives of the epidermis, such as nails, hair, sebaceous 

 glands, and the lining of the glands connected with the digestive 

 and genito-urinary systems. 



These tissues are composed of cellular and intercellular 

 elements and perform various functions in different parts of the 

 body. In the skin where they constitute the epidermis, they 

 protect the delicate surface of the true skin beneath; in the 

 alimentary and genito-urinary canals they aid in secretion and 

 excretion; in the respiratory system they preserve an equable 

 temperature, while in all internal parts they yield lubricants. 



These tissues are characterized by the preponderance of the 

 cellular over the intercellular elements. The intercellular 

 structure consists of a cement substance which holds the cells 

 together and through which the food for the cells is absorbed. 

 They contain no blood-vessels and no nerves. The tissue 

 usually rests upon a basement membrana, or membrana propria, 

 which is a modification of the connective tissue beneath. 



